I tried my heart out searching through a few Japanese sites trying to find some link, but to no avail (someone else can try that path if they want)...So, instead I just hit up the Google News section for August 2006 (the time in which the first Chrono Cross spike seems to occur)...
The main thing coming from Square-Enix at that time was the launch of the FFIII DS remake and also news about them licensing the Unreal Engine 3...which made me think...didn't one of the CT fan remakes use a version of the Unreal Engine?
The second, longer running spike, or increase in interest occurs around November...which would make it 5 years after the the month of it's Japanese release (August was it's NA release, though that would only be 4 years...coincidence?)...
Looking at
the last 12 months, it looks like Radical Dreamers had a fairly large spike there (surpassing Chrono Trigger) at the end of September...do we know the month of which it was first available for download? I couldn't find that information...
RD also had it's first spike in September of 2004 where it ALSO beat out Chrono Trigger...Hmm...
I have NO IDEA why Koga & Tsukuba both have such large interest in pretty much ONLY Radical Dreamers...>_> Koga accounts for what looks like 5x what any of the others are putting out (outside of Tsukuba, which has about double)...What's so special about those places?
Also, just for kicks, I decided to see how the series does comparative to the two Square-Enix juggernauts "ファイナルファンタジー" (Final Fantasy) & "ドラゴンクエスト" (Dragon Quest).
Here are the results. As you can see, none of the Chrono series is even close to either of them. >_>