Most of the necros I've seen here weren't of the sort that contributed a lot to the original thread but rather of the sort that caused a lot of confusion.
Case in point:
Reviving a release thread from 2015, making it seem like this was news about a recent release. (In this case, one could even consider it a valid question, but the way it is delivered is still questionable, IMO, regardless of whether it was thoughtless or intentional clickbait.)
Or replying to a post someone made ages ago as if they had only just said it, while the original poster most probably has long since moved on. It leads to more people mistakening the thread for an active discussion that requires input, without paying attention to what has already been said before and WHEN. In some cases, it's imaginable that new posts can still contribute something worthwhile, but from my experience these cases are an exception, not the rule.
I always wonder how these necromancers even find and pick the threads they post in. If it's an honest interest without any intention of spamming or trolling, do they just type keywords they are interested in into GOG's subpar search engine, in order to find a place where they can share their opinion on them? Or do they make it a hobby to read the forum in its entirety, chronologically, from oldest to newest posts? *honestly puzzled*