Why kill off everyone we knew in CT?

[Thought]

Perhaps the simplest reason for killing off everyone we knew in CT (while not definitely killing a single one) is simply to explain why they aren't worked into the story, and it puts more emphasis on the current party. If Crono & Co was around, really, would there have been anything for Serge to do?

Given that for everything that happens, there are at least a million different ways the course can go, the operative theme of CC was an infinite amount of dimensions, though you really only travel between two, due to Serge's special case.

Actually, CC seems like it argues for a very limited number of dimensions. Indeed, only two are known to exist for sure, with the reptite/dragonian dimension being unclear if it is a full dimension or temporal leftover from a previous change to the timeline. The game places the cause of the split fairly squarely on the 50/50% chance of Serge dying or not, something that doesn't seem like it would be overly common. But as the good Mr. Bekkler pointed out, there's only one dimension that we even know they don't exist in.

The year 1000 A.D. was a little too peaceful.  We knew nothing about Guardia's founding or why it was important enough to establish its own calendar.

It didn't establish its own calendar, though to be fair it does appear from 600 and 1000 that the kingdom was roughly founded around the turn of the era, give or take a century. As for it being peaceful, you are forgetting that the mystics tried to dethrone King Guardia XXXIII. And that Guardian military tech has decent enough funding to create the dragon tank (indicating that there are other militaries out there to potentially use it against).

[Lennis]

As for it being peaceful, you are forgetting that the mystics tried to dethrone King Guardia XXXIII. And that Guardian military tech has decent enough funding to create the dragon tank (indicating that there are other militaries out there to potentially use it against).

My impression was that the Mystic plot against King Guardia XXXIII was a personal vendetta by Yakra rather than an organized effort to topple the Kingdom.  And on the subject of the Dragon Tank, we never got any clue in canon that there was a potential enemy to use it against.  Of course, this lack of clarity is one of the reasons I don't like to rely solely on canon to discuss the world of CT.

[Thought]

True enough. But I think you get that my point was mostly just that there were enough ripples in 1000 to indicate that its peacefulness seems to stem more from being underdeveloped than intentional.

[Lady Marle]

I wonder if Guardia ever went through some minor wars, maybe even Civil Wars between Guardia and Porre (hence the conflict in 1005) in between 600 and 1000 AD.... I mean... did anyone not notice an entire town is no longer in the souther continent in 1000 a.d? Theories on what could've happened to it?

[Wolf Kanno]

Perhaps the simplest reason for killing off everyone we knew in CT (while not definitely killing a single one) is simply to explain why they aren't worked into the story, and it puts more emphasis on the current party. If Crono & Co was around, really, would there have been anything for Serge to do?

This was always my thought. I usually find that direct sequels don't work out so well for stories, cause often the original cast has already achieved everything they needed in terms of plot, emotional growth, and goals. Creating a sequel story that has a new threat just as menacing as the original is kind of hard to swallow if you ask me and tends to cheapen the experience of the original. But... if you were to make a direct sequel about a new cast of characters you get the benefit of still using the resources from the original story while also creating new complications that don't directly clash with previous events.

If CC did one thing right as a sequel, it was the fact it made the idea of a Chrono sequel appealing. The original CT was a pretty complete package beyond a few loose ends that fans could have easily come to their own conclusions about (The Entity, Schala, and the fate of 2300 A.D.) but CC turned this all upside down and now has fans clamoring for a Chrono title that would fill up all the loose ends. Before CC, I couldn't think of an interesting story that would involve Chrono, Marle, and Lucca but CC establishes a scenario that makes the prospect of them returning that much more meaningful.

There is also the fact that there was really no way that CC could live up to CT. CT was kind of a once in a lifetime kind of game and making a sequel to it that would actually make all the CT fans happy is pretty unrealistic. I feel Kato and Tanaka had the right idea of scrapping all but the fundamentals of CT and building something new with it. Even if they had tried to make a more true sequel, their was a pretty good chance it wouldn't have survived through the hype it would have had. Kato might as well have built the story he wanted to make instead of trying to pander to unrealistic expectations. That's why I feel CC is successful, it works as a sequel because it relies so heavily on the events of the previous game to make sense but it is so radically different that it is difficult to really compare it to CT.

[Xenterex]

My impression was that the Mystic plot against King Guardia XXXIII was a personal vendetta by Yakra rather than an organized effort to topple the Kingdom.  And on the subject of the Dragon Tank, we never got any clue in canon that there was a potential enemy to use it against.

There may be an aspect of personal vendetta to Yakra at that time, but his methods are similar to, though improved, upon the attempt of the 600 era Yakra in his attempt to overthrow the kingdom.  In my mind, I had figured the fall of Guardia to not be because of Porre attacking Guardia, but Dolton organizing the mystics from medina (and wherever else) to overthrow guardia.  With the mystic's abilities to disguise themselves as people, combined with a few intentional slips (like Yakra) mixed with some gossip and Guardia could be up in a 'red scare' of their own. Things escalate and a scare becomes a civil outbreak of terror and eventually Porre (and Lucca) use some firepower to clear things out.

If CC did one thing right as a sequel, it was the fact it made the idea of a Chrono sequel appealing...

 
I will say I really did dig the title of the game when I first saw it.  As like the example above, however, I've been one of the sort of a fan that wanted more from CT and searched for ways it could continue.  I do share some of the sentiments of the OP for this thread though, and while my 'evidences' over the years are probably more suited to simply appeasing what I already think, I would say it does seem more likely to me that Kato's approach to CC (and possibly even RD) was indeed that he was trying to "prove something".  I think if he'd been less focused/obsessed on this superficial dilemma (as I see it) of indeed trying to prove something (or at least what I perceive he was trying to prove) and gotten some more critique on his work during development, CC would've been a much more balanced (and successful) sequel, and not a bi-polar product with an identity crisis. 

[Thought]

I wonder if Guardia ever went through some minor wars, maybe even Civil Wars between Guardia and Porre (hence the conflict in 1005) in between 600 and 1000 AD.... I mean... did anyone not notice an entire town is no longer in the souther continent in 1000 a.d? Theories on what could've happened to it?

Did you notice it seems to reappear in 1999?
Alas, Dorino might have just been cut from 1000 because it served no purpose, or it might have had a reason for going away, but they tell us nothing.

[Acacia Sgt]

Problem would be, since these are Time Peroids, you just can't remove something that you show both in it's past and future from the perspective of the lacking part, and get away with it without an explanation.

So yeah, either they really didn't show for serving no purpose and expected us to settle with that, or that city in 1999 is just some other that got established where Dorino used to be.

[Thought]

Sure you can. You just confuse fans.

[Mr Bekkler]

Obviously, it's "New Dorino" or perhaps even "San Doritos(TM)". After all, we're talking about the year 1999. 

[Lady Marle]

Obviously, it's "New Dorino" or perhaps even "San Doritos(TM)". After all, we're talking about the year 1999. 

AHAHA It's NEO DORINO!! XD

[Lennis]

I wonder if Guardia ever went through some minor wars, maybe even Civil Wars between Guardia and Porre (hence the conflict in 1005) in between 600 and 1000 AD.... I mean... did anyone not notice an entire town is no longer in the souther continent in 1000 a.d? Theories on what could've happened to it?

Well, in my version of events the original animosity between Guardia and Poore can be traced back to their respective founders - Cedric Guardia and Anteaus Poore, who fought a three-year-long war to determine the undisputed ruler of the Zenan continents.  (A nod to Crimson Echoes)  But in truth, the real falling out between Guardia and Poore would happen 900 years later over matters of unequal taxation.  Queen Laramie was a somewhat cold ruler who instituted a policy of greatly reduced taxes for the wealthy provinces of the north to spur growth, but left the tax rates of the poor southern provinces largely unchanged.  When Laramie passed away in 891, the people of Poore celebrated in the streets, prompting a very harsh response from Prince Levin.  Using new weapons called muskets, Levin's forces put down the unrest very quickly and killed thousands in the process.  It was one of the only times Guardianians would shed one another's blood, but it would not soon be forgotten.  The underground Poorean Independence Movement was established soon after the massacre and quietly gained strength over the next century.  By Marle's time, there is open talk of secession, and the movement is looking for a spark to fan the flames of revolution.

On the subject of Dorino (St. Dorino), I think it wasn't included in the modern-era of the game due to relevancy.  Of course, the city should still exist, there's just nothing to do there.