I think you have a good point about flairs. The lack of flairs is especially noticable in sports communities. On Reddit, a lot of sports subreddits would have flairs of team logos, which set up for a lot of friendly teasing between fandoms. The lack of flairs in Lemmy takes away the teasing because nobody knows who supports what fandom.
There’s also a similarity between cat communities and sports communities in that there’s probably not enough people to support individual team communities similar to how there isn’t enough people to support more focused cat communities like one orange brain cell.
Easier sign up. On BlueSky you can just sign up for an account and go. You don’t have to worry about picking an instance or anything like on Mastodon, which can be a bit off-putting for someone not familiar with federation.