You’re correct here. Even historically federated services, like email, are referred to by grandmas as “my AOL”. They don’t even think about the fact that others

You’re correct here. Even historically federated services, like email, are referred to by grandmas as “my AOL”. They don’t even think about the fact that others don’t have AOL, they just grab a name out of an address book they’ve been building for the last 20 years. Just because email exists as a federated thing doesn’t mean existing users could use it if they had to sign up for it again.