They don't have to have everyone on them to be good. In some ways it's preferable not to. Reddit was far better before the Digg migration, and we might already be living in the golden years of Lemmy and not even realize it.
It's true, that's the advantage of a larger user base. But when I compare my homepage of Reddit after 15 years of refinement to that of my lemmy homepage after 1 year, my lemmy one is way better. Most of those niche communities devolve into memes and nonsense like the same questions being asked over and over and over again after a while. Great for searching, but for actually getting content on a regular basis from, mostly a waste of time.
This is true, it’s like other platforms that value content creation rather than value, so people keep repeating the same thing. I haven’t worked as a moderator ever so I don’t know what’s possible or impossible, but I think many of these problems are a result of poor moderation though.
Sometimes moderation needs to be a bit unpopular to have the community work in some way.