I think some of this may be the default Active sort setting for the all/federated feed keeping some communities and their posts around the top. Might be mistaken, but my understanding is that it primarily elevates upvoted posts with recent comments, leaning on recent comments for keeping it visible.
Problem is, that means some posts that may get a decent amount of upvotes but no or few comments may gradually get buried, only rising to the top briefly or on some slower days.
I think as a result of getting buried, some may not see the other stuff they might want to talk about to comment on, and besides that, I sometimes get the sense there are a lot of lurkers around here, voting on stuff but otherwise not commenting either for lack of anything to add or not wanting to risk getting into arguments (if not both).