That's a good example. In a way, e-mail was the first federated social network, and nowadays there's no critical UX issue with "there's too many e-mail provider

That's a good example. In a way, e-mail was the first federated social network, and nowadays there's no critical UX issue with "there's too many e-mail providers to choose from, there should be only one GMail for people to sign up to". The only difference is that e-mail is "obvious" and Mastodon is new.