Why is Necro'ing bad?

[Snowhawk]

I asked this question on another site with even more ridiculous rules about Necro'ing posts than here. (Seeing as here its just frowned upon by GMs)

Why is it so bad? If the topic is relevant why is it bad to bring it back into play? We already have to search to see if the topic was brought up, (most people don't but are always linked by older people when same topics arise) and have to make new posts repeating everything that was in the original topics just to start the same discussion over.

If the post is already there and there is a general interest in it why is it looked down upon by GMs? And since it is why don't the GMs Archive anything that hasn't been touched by anyone in over a Month? All you say is don't revive possibly relevant topics that could be in the best interest or at least interesting for various players. Seems like a pointless endeavorer and a lazy way for the GMs to tell us to just shut up.

(Rule on the other site is litterally. Post in any topic that is over a month abandoned (No new posts) and your account gets a 3 day suspension and the topic gets locked to prevent other people from posting. Unless a topic is locked you cannot start a similar topic, it must be discussed in that thread. Any similar ones are merged into the older ones and your account receives a strike against it for breaking the rules and all the new posts must be made in the merged thread (even if the original is a month dead))

This actually seems to happen on a lot of various forums. I run one and we revive topics that have been dead for an entire year if they were not closed by Administration simply cause its easier to restart than having to repeat everything over and over again.