Also #bluesky essentially has no usable migration. Because where to? You can also download all your data in #mastodon and #twitter. In a format anyone can build an app to use. In #mastodon you can at least change servers. With #bluesky you can't even do that.
Bluesky

Bluesky Social
#activitypub is the reason for these advantages of #mastodon. The truly #decentralized architecture makes the barrier to entry low. In #atproto, on the other hand, relay and #moderation are not decentralized, but each alternative provider processes and moderates the entire social network.
Bluesky

Bluesky Social
This architecture of #atproto will realistically ensure that there will never be real alternatives to #bluesky. In other words, #atproto only appears to be #decentralized on paper. In practice, it is probably trapped in #centrality.
Bluesky

Bluesky Social