1. The platform is outright hostile to discovery. You generally can't even index posts in a search engine. This is not what I want, at all.
2. Moderation is awful. Letting individual servers control moderation at their whim is not what I want. In contrast, Bluesky's idea of labelling services and opt-in moderation sounds amazing.
3. After point 1, it probably goes without saying that Mastodon is outright hostile to algorithms. While I agree that algorithms can be very problematic, Bluesky's approach to opt-in algorithms is an interesting approach.
4. I think the ship has long sailed on Mastodon. It's failed time and again to gain enough critical mass for non-tech people to adopt. Clearly the combination of above issues, or even maybe the confusion of onboarding, is too much.
Overall I'm glad Mastodon exists, and perhaps Bluesky wouldn't be what it is without first seeing what worked and didn't work with Mastodon.