It's amazing people on other forums get so worked up about this. It really has nothing to do with optimal forum usage. It's all about promulgating means of social conformity. "THIS IS OUR CUSTOM!! TO BE LIKE US YOU MUST ACT LIKE US!!!"
Bosh.
There are a few plausible reasons why people don't like thread necromancy beyond conformity; I've never really seen other board try to force it upon each other and I have seen many other boards that have nothing against it. It just seems like a rule a lot of people enjoy...
Personally I couldn't care one way or the other; it doesn't seem like that big of an issue, as long as people respect the rules of the board they are using.
You've obviously never been to Qhimm. Thread necromancy is a dire sin there and you will have your head torn off because of it.... then reattached so they can yell at you.
On many forums there is a reason to avoid it... a simple one. They don't get new members often and whenever everyone has said their piece, it is the end of the discussion and no new information will be brought to light. Most fora do not have an intellectual basis at all...
Most threads that get revived are threads about "how do I ____"; "can I have ____"; etc. And whatever the consensus is at one time, will always remain the consensus. It is also a deadly sin on such fora to create a new thread about that topic (instead of reviving the old one) as well as generally talking about it at all.
On many fora the basic concept is this:
"If you weren't here the first time this was discussed, you have no right to know anything about it, so don't even ask."
There are also varying rules about multithreading... Some places encourage the creation of individual threads for each person that has a question about any given topic...and discourage bringing your own concerns into someone else's thread entirely... while others are the opposite, and believe that any topic should have one and only one thread, and everyone should talk about it there... This is usually accompanied by the thread burial rule... ending up in a finite-information-sink... once the thread dies, it is assumed (or rather, militantly
enforced) that no new information did, does, will, or CAN exist on the matter. Ever.
This is why people get so stuck up on thread necromancy... it is not generally well received in many many fora, and this conditions patrons into trying to enforce it by habit.
The abused become abusers in turn.
On this forum in particular, it may be the presence of the notifier that mentions the age of a thread and that one might reconsider posting in it... It's all about mixed messaged. The rules say it's ok; the software still discourages it.