The major, terrible tech walled gardens have done such a good job of convincing people that things shouldn't interoperate that it's hard to explain to people what federation is. For my generation it's easier to explain it as "like email." That's because most of us still care about email and have used email enough to find the idea of non-federated email ridiculous. We accept that sort of garbage all over the place though.
For the next gen nobody really used email enough for them to use that as an anchor for how things could be. They have no concept of a world where the data is there's and communication is federated by default.
We come here in search of a place to express our thoughts outside of the direct control and surveillance of unaccountable, mega-corporations. There is no common theme that binds us other than these being the bonds we've chosen rather than those that have been chosen for us.