As a tool for forming communities, Lemmy’s mechanics work just fine.
But the process of federation - combined with the prickly nature of certain administrators - means you can have a lively and robust community in (hypothetically) the far-left transgender tankie community that pioneered the application. But then that gets abruptly cut off and squelched in a more popular forum by some late adopters who hate their politics more than they enjoy their technical savvy.
Lemmy.world has a bunch of memes and political screeching because that’s the kind of user its admins choose to encourage. Other communities have more practical interests. But they don’t draw the same kind of crowd, so you won’t see them on the front page of this site, particularly if you only browse Local.
They’re an idea that big forums are actually awful and you’re better off in smaller communities.
Mostly, it’s a pain because it can be hard to find some escoteric bit of knowledge or expertise when you don’t have a Reddit sized forum to troll through.
But that’s where spaces like Discord excel. Nice, tight communities of hobbyists and specialists who are routinely online and regularly churning out useful content.