I never managed to get into mastodon because mastodon isn't a single space. It's a bunch of separate, linked spaces. Which server you're on matters a lot, and I never found one that really had the vibe I was looking for.

Bluesky, though, is one big pool. There's no seam between servers. The experience is much nicer.

Also, bluesky caught on among my peers in a way that mastodon never did, which was always going to be the deciding factor. I imagine not having to "choose a server" was a big part of that.