Your data, such as your posts, likes, and follows, needs to be stored somewhere. With traditional social media, your data is stored by the social media company whose services you’ve signed up for. If you ever want to stop using that company’s services, you can do that–but you would have to leave that social network and lose your existing connections.

Source: Bluesky: An Open Social Web

I hope this means there will be a Mastodon adapter for Bluesky and vice versa.