Mastodon’s (and other fediverse alternatives) barriers to mass adoption are two-fold, I think.
First, and probably the most important, is reach. If your peers are on Twitter, you’ll post there, even if the level of interaction is higher on Mastodon (which seems to be the case, but n=1).
The other one is UX. Federation is amazing, but it’s not something most users want to worry about. Mastodon is doing a great job, but the issue of picking a server and trouble finding people remains.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!