Bluesky uses “AT protocol”, not ActivityPub. Ironically the former is trying to federate as well, but still it’s a different protocol altogether (so it would federate within its own network, as in people could start up their own Bluesky instance). Despite that, some people tried building a bridge between ActivityPub and AT, but there was enormous pushback, driven in part by ideological differences between more serious Mastodon users and the more casual X/Twitter style user (picture a Reddit mod, now halve their IQ, and I’m just joking bc I’ve never had a Twitter account so I don’t truly know what that filth is like to have to wallow in:-). Anyway, MBin is able to connect Mastodon to Lemmy bc they both use the ActivityPub protocol, but AT is a different protocol.
A lot of things allow you to export your settings, but nothing that I’ve heard of allows you to import your posts and such - and therefore truly migrate - your account from one place to another. Therefore the whole federated concept has been oversold - as in, “if you don’t like a place you can leave it and go somewhere else”, the same as anything else in the entire history of space and time (divorce, immigration, quitting your job, etc.). But if you do, then you lose everything - all of your follower base, which for like an author is impactful to their actual career. Hence why so many are so reluctant to leave X, despite the Musk having taken over (and the smell permeating the place now, to where most of their followers are gone as well).
It’s the same reason why “everyone still uses Windows” (I don’t): herd mentality, and also, like using Querty (that one I do), holding onto the past bc of not wanting to pay the price to have to switch.
