In total the fediverse is stable or slightly growing. ActivityPub is how fediverse instances exchang information. More and more platforms are getting stood up and there are also a bunch of instances of those platforms.

Platforms are things like Friendica, Lemmy, Mastodon, PeerTube, Funkwhale, Hubzilla, Misskey, and now Pifed. Instances are things like lemmy.world and sh.itjust.works.

This approach was intentional. No single platform or service controls everything and if someone starts misbehaving it's easy enough to go elsewhere.

That's not to say there aren't downaides. We have a ton of communities for similar topics on different instances and/or platforms. Each of these communities need to be moderated, have an active user base, etc.