I think there should be some incentive for that, like make those kinds of comments a spotlight or something. Maybe make a community called “late replies” that showcases the best such replies, or have a rule saying they grant free karma (in Reddit’s case).
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.)
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.
Its not a global bump, but it does bump it back into conciousness for the person being replied to. Ive had it happen a few times on lemmy, and its always so confusing because i had completely forgotten what i had originally said.