thing is though there are also many existing alternatives to Mastodon already on the Fediverse, so why fork it?
Because you still don't know there's more to the Fediverse than Mastodon. I think at least every other Mastodon user doesn't.
Or if you do, you think it's all just alternative graphical frontends to the same stuff that Mastodon is.
That's why people still develop stuff only against Mastodon. Bonus points for slapping "Fediverse" on it.
That's why people still fork Mastodon to add features that are available just about everywhere else.
And that's probably why @The Nexus of Privacy wants to fork Mastodon into what he seems to think will be the absolute pinnacle of privacy, security and permission control in the Fediverse, blissfully unaware that it's not only an attempt at re-inventing the wheel, but a far cry from what @Mike Macgirvin 🖥️ has been developing since 2012. That was four years before Mastodon.
Seriously, I keep seeing people wish for features in "the Fediverse" (read, Mastodon), features that are readily available elsewhere in the Fediverse. Some of them have been since before Mastodon was even made.