I think part of the problem was the content began to congeal into the same kinds of posts. Even the exact same posts. The reblog feature meant a lot of content was just being endlessly re-posted, sometimes with a comment and sometimes not.

So there were much fewer unique posts, and thus less reason/interest to invest time into making new posts.

At least this was my perception as a somewhat regular user among friends several years ago and why I ended up stopping using the platform.