There really needs to be something done about it tbh.
You can't exactly "accidentally" necro something, these people are straight up going back oogles of forum pages looking for these threads that are obviously long dead by that point and posting in them, not paying a lick of attention to the last comment's date which is NOT HARD TO MISS IF YOU PAY ATTENTION.
I'm in another forum that has a rule to not necro threads that are over a month old in inactivity for the most part unless you're the OP and have a VERY good reason to (As the forum in question is rather active) unless it's very specific boards like RP and Creative ones where the limit doesn't apply. And if they do pass that limit, just make a new thread of the same topic so that necroing is avoided (Regardless of how repetitive it is). And I have seen new people do this shit all the time, it ends up with them getting locked right after and the admin of the board having to tell these people to not necro threads that are past the date in terms of the last bit of activity on it and to check for the notice stating to not necro WHICH IS RIGHT AT THE TOP OF THE THREADS IN QUESTION before posting. This happens more than it needs to. Yet they don't do that.
It may not seem like that big a deal, but it's annoying, and alongside all the things Evil has mentioned, there are things ON THE FRONT PAGE OF THE BOARDS or at least the first few that are seen active that can be bumped without issue, rather than some thing made in 2015 or something that hasn't been touched in a fucking year. Goodness people CHECK the last comment's date time it was made before you go being all "Uhhh is this still being made?" when it clearly ain't with how dead it has been. It doesn't take but a second to check before posting. >.<