This week, I went over to Bluesky and asked people who'd left Mastodon why they left, and lots of people told me. I grabbed the replies and crunched them and wrote up a summary. I think it's really interesting and often kind of wrenching.
https://erinkissane.com/mastodon-is-easy-and-fun-except-when-it-isnt
Rather than trying to head off the unusual unpleasantness about clout-chasers and the ritually/technologically impure, I will just say this:
I wrote this up for fedi people who are actively curious and interested in other people, and I'm not going to worry too much about how it lands for those who aren't.