In case it helps you understand: barriers of entry to Mastodon, from my perspective as an ex-Twitter user and current Bluesky and Mastodon user (note it took me 4 tries over 5 years to actually “enjoy” Mastodon)

• Lack of content discoverability: Bluesky has programmable feeds and starter packs (although the latter is pretty flawed), Twitter has The Algorithm. When you first create a Mastodon account, you’re not given much.
  • The primary reason Mastodon “stuck” with me on the 4th go around was this. I manually imported a bunch of my connections from Bluesky.
• Choosing the right server: on all my previous attempts, I was overwhelmed by server selection and went with generic all-purpose instances. Having a local timeline with things that might actually interest you is very helpful.
• The network effect: I don’t think I really have to elaborate on this one

Bonus things that probably don’t serve as barriers to entry but are real issues for active users:

• Lack of features: it’s not possible to search for posts on ActivityPub at any reasonable scale. I don’t know all my Mastodon lore and think I’ve heard that search was intentionally not made good in the past for privacy or something, but if you’re posting something on the “blast my posts everywhere” protocol, well… it’s still out there.
  • There’s also no quote posts, which haven’t been implemented for similar privacy/anti-harassment reasons. But instead, other software like Pleroma works around this by simply giving a link to the original post—the worst of both worlds, bad UX and not even an option to attempt to detach or prevent quotes.
• Fedi meta / sudden defederations: If you picked the wrong server—or any of your friends did—and you end up with a tempermental admin, you could unexpectedly lose contact with each other due to defederation, and you might not even notice.

This is not to say other platforms are perfect. There are plenty of things I don’t like about Bluesky. This comment is specifically about Mastodon.