There are reasons already outlined, but beyond that, even if they were all equal and users picked them completely randomly, it prevents any single instance and therefore any owner or company hosting them from taking over the whole thing.

For example, with Twitter or Reddit, if they decide they don’t like something and shut it down, that’s it, it’s gone. And with everyone locked into the ecosystem, you can’t really just pack up and leave.

The fediverse on the other hand is essentially immune to that: the community can simply be moved to another instance, and users can migrate to different instances while still accessing the same content.

For example, lemmy.world defederates hexbear and lemmygrad, but I can access all 3 of them at the same time from my instance. There’s also weird cases like lemmy.ml defederating ani.social, but I still can access those two from my instance as well no problem.

The admins are empowered to cut off instances they don’t want on their server (for example, many don’t want anything illegal or legally grey because they just don’t want to deal with legal problems) and curate the experience for their users, and if it’s not for you well you can go elsewhere without missing out.

Then there’s fun stuff like different legal jurisdictions: Reddit being a US company has to comply with US laws even if the user is European or Australian or Chinese or Japanese. With the fediverse, someone local to all of those can make local instances without being completely cut off from the rest of the network, only subsets of it but still access things like programming.dev.

And thus, nobody can really take it away from us. Nobody can really shut it down. It’s also somewhat censorship resistant because now you can’t just ban Reddit, you have to keep track of and ban every Lemmy/Kbin/Mbin/Mastodon/Pleroma/Friendica/PeerTube/Sublinks instances in existence.