I use Lemmy, and while federated social media might seem like this up front, a good comparison is dorms and classes at a large university.

Every dorm/housing and school program has its own vibe and attitude. Your student ID gets you in to all of them, but you live in one dorm building in particular, let's call it Jones Tower. There might be some seeming overlap between buildings - maybe Dinkley Hall and the Rogers Building both have Engineering floors, but they're not the same at all. You can cross-list classes between the geology department and theater school and gerontology, that's cool. You can have friends that live in Dinkey Hall and the Blake Apartments, and they can all go anywhere they want.

Is it a mess? Not really. Is it as plain and one-size-fits-all as single-story high school like Facebook? Not at all. Does it take time to understand how to sign up for a cross-listed class? Sure. To some it's worth it to be there, and plenty drop out because it's not for them, and that's fine. IMO, the benefit is the barrier to entry. It's not for everyone and doesn't need to be.

Threads added federation, but only Mastodon servers are connected, and not all of them - this is like Threads is the private medical school across town that lets grad school students from the Fediverse Uni come over for specific classes.