NNTP is also great but most people can not afford individually to mirror entire binary groups and most ISP's no longer perform this so most people just use commercial news feeds if they want binaries or one of the free NNTP / Usenet providers if they are just using text. People can certainly peer with some of the free providers [1] and probably should to reduce the risk of people being censored. Much like IRC people can create their own little private or semi-private linked NNTP servers to replicate a distributed thread based forum of sorts.
[1] - https://www.eternal-september.org/index.php?showpage=peering
Where-as with Bluesky/ at protocol, most folks are on Bluesky servers, yes. But there's a very strong credible exit case where you can leave the Bluesky servers & just do your own thing. And follow whomever you want to follow.
Bluesky / at proto creates a trust mechanism beyond DNS, creates an identity that can be moved around between hosts or replicated outwards in a verifiable way. I dig ActivityPub, and have been a long time http enjoyer, but it's not ideal imo for social media to need to be so coupled to such strongly DNS based client-server systems.