You're not the only one who sees it that way. Historically the Fediverse was always multi-protocol but some people don't think it shojld be today. I talked about this view some in https://privacy.thenexus.today/is-bluesky-part-of-todays-fediverse/
"Anyhow, if Evan and Eugen and SWF and fediverse.party want to choose a definition of Fediverse where history stopped with Mastodon's 2017 adoption of ActivityPub, erases earlier Fediverse history, and ties the Fediverse's success to a protocol that has major issues ... they can do that. "The Fediverse" means different things to different people. It's still worth asking why they choose that definition."
Kuba's link i that thread is good, it looks like there's currently about 370 PDS's -- Bridgy Fed got an exception from Bluesky so is the only one that currently has more than 10 uses. https://blue.mackuba.eu/directory/pdses I know some people who just run the open-source code for Bluesky's PDS (which is pretty straightforward) and some run other implementations.