What does Bluesky have that Mastodon doesn't?

I mean, even Neil Gaiman is far more active on Bluesky than he is on Mastodon, even though probably a greater proportion of his fans are on Mastodon, and he was on Mastodon well before Bluesky. So he's getting something from Bluesky that he isn't getting from Mastodon, and that's noteworthy.