I see a lot of comments saying that people comment, but I'll occasionally post videos when I see them come out, get zero responses, and will see the same video on Reddit with thousands of responses. These aren't small communities either - the videos community on lemmy.world has thousands of subscribers, but few videos have any comments.

I don't think it's necessarily an issue with people not posting enough. I think there just aren't enough people to sustain a social network with thousands of communities.