I think the term would be "necrobump"

That's from old school forums where posting to a thread bumped it back to the top of the feed and thus thrust old info prominently into everyone's view again. You won't get that same bump effect with most sorts on Lemmy. ("New comments" sort might work like that though? I'm not sure exactly how that's handled.)

otherwise everyone has moved on

It's pretty rare to get much of a response even after just 24 hours or so -- not just in terms of comments, but even for upvotes. I think after that point, posts are usually so far down people's feeds that almost no one sees it any more. That probably also discourages most people from replying since basically no one will see it. (Maybe the poster of the thread or comment you're replying to will see it, but probably almost no one else will if it's more than a day or so old.)

Some people do dig through community archives and/or user profiles -- particularly after a new thread is posted -- and they'll occasionally upvote old posts, but they very rarely comment.

I'm not against necrobumping in certain contexts. If I have a tech support question, I can promise you I'm still clueless after 5 months. Also a niche creative project can take over 5 months to find it's audience, and creators are usually happy to hear feedback.

Oh man, that brings back memories of necroposting on old IPB forums

I still get necrobumps from reddit on year-old comments despite having left reddit. It's weird.

People only posting on new things makes a place seem less like a community and more like people are just being trendy.

Side note, necrobump sounds like a great name for a heavy metal band.

necrobump

What a horrible name for "people responding to a thread that is older than a mayfly".

Suggesting something a few months old is "dead" is especially churn-y; like "Ahmahagawd, that thread is, like, SO last-heartbeaaat". Ensure the voice dissolves into an indolent vocal fry for best effects.