Well, Lemmy is really not good at pushing new content/new posts and/or new communities to people. For many of us, that might be a boon: less algorithmic shenanigans, less "steering" of the user. Yet, if you are not a user who likes to actively seak out stuff, your feeds will look stale and slow-paced very quickly. There might be new stuff,.but the feeds struggle to find a middle ground between "only the upvoted stiff you subscribed to", "the always same server wide top posts" and "bleeding edge new stuff". It's also very reluctant to sprinkle on new communities.

I think that's a main contributor to the decline.

For the record: kbin is more liberal when it comes to that sort of stuff. So if you like a more active feed, you might want to try kbin. If you like your feed to be controlled by you more, use Lemmy.