1 - The UI is sorely lacking in features compared to akkoma/misskey and soapbox
2 - Eugen is marketing to the world that Mastodon is the fedi and being dishonest and political as usual.
3 - The rampant defederation and blocking by Mastodon instances is getting out of hand and I don't want to be associated with it.
4 - The Twitter exodus is corporatizing the whole thing and it's losing it's homegrown FOSS feel.
5 - Did I mention the UI sucks? Literally the only thing I like about it is the music player.
6 - The fediverse is not Mastodon, this is misleading and many people are joining Mastodon for the wrong reasons.
If things change, then so be it. But I'm happier engaging with ActivityPub using other software stacks. That's the beauty of the protocol, all the options and the freedom to do what you please.