I’ve used both fedi and Bluesky so I might be able to chime in, here. I have both my praises and my concerns for both fedi and Bluesky but I’ll probably post that elsewhere.

Bluesky is an implementation of a separate federated protocol called Atproto. It was initially designed for Twitter but after Elon’s acquisition it has spun off into its own public benefit LLC, with the creator of XMPP in the board of directors as well as former Twitter CEO Jack Dorsey. I don’t know if Jack is still on it though after he got bullied off for being a crypto-bro but it doesn’t matter, the code is open-source and you can spin up your own server.

The “invite-only” part of Bluesky is Bsky.social, the flagship server instance for Atproto, but there are servers being spun up waiting for federation and in the future, bsky.social will be open to the public. AFAICT they want to get the federation right before deploying it to bsky.social, rather than just winging it and having federation break. There is a federation sandbox for developers to help get the federation just right before rolling it to production. They have considered ActivityPub, which powers the fediverse, but they wanted account portability which neither ActivityPub nor the software that powers the fediverse were intended to do. Follower migration is a thing on fedi but not post migration, and they want to solve that problem.

For me, Bluesky is much busier than fedi. Furry artists are popping off a lot more on Bluesky lately. One thing people tend to ignore is human behaviour. Most people want a place where they can chat to their friends, that’s why Discord is strong to this day even though XMPP exists. Truth be told, only tech nerds care about federation, most other people just see it as unneeded complication. Add to the air of elitism that’s in this very post (not from you, fyi) and which is across the fediverse, and yeah. I can absolutely understand why some people are choosing Bluesky right now over fedi.