Nobody cares about protocols, except maybe the handful of infosec nerds on Mastodon. It's about a middle school-level rearranging of friend groups. A VIP lounge where they only hang out with their own.
There was an exodus of a small subset of users, and BlueSky was there like an abandoned building that was squatted. It being invite-only added to the exclusivity as invites were passed amongst like-minded peers online, further adding to the echo-chamber.