They can have it. We just don’t want to federate with them, which doesn’t prevent them from having their own instance all for themselves.

I don’t think so. It’s probably what keeps it small and more personal. There is also the notion of responsibility: if a person I invite causes trouble, it’s potentially on me. Maybe not on the first infraction, but if one invites 20 spammers/cryptobros/venturecapitalists, it’s reasonable to block the inviter too.

I’m not arguing one way or another (that’s not my decision anyway), but I can understand why they do this.

You’ll probably enjoy Lobsters: https://lobste.rs/