Everybody talks about “why not Mastodon” in the comments of these. I thought about that for a long while back when I used Mastodon, and I have an answer: discoverability. ActivityPub does not make things easy to find, which makes a Twitter-like service even more like screaming into the void. It effectively becomes “bring your own audience,” and tends to only amplify the voices that are already the loudest, though as a consequence of the backend, rather than a malicious choice like Twitter.
Dodi, fitgirl, etc.
Good links can be found in the mega thread stickied to the community or on FMHY.