1) A Twitter clone without the political baggage and chaos of the current Twitter ownership.
2) A vastly overengineered distributed software system with a strong ideological commitment to federated design.
There's no inherent relationship between the two, but a lot of the people who run 1 are heavily committed to 2, and so end up sowing a lot of confusion about it.
I would wager that most Bluesky users don't care about it being decentralized, and in fact want a lot of features (soft block, private blocklists) that the federated design makes impossible.