Eryk SalvaggioMastodon setting up the servers as “identities” is a weird move. Is someone gay or an artist? Are they interested in tech or cake recipes? Probably all of them! The server-as-identity is a counterproductive and highly artificial way of presenting the idea to the public, and its doing more harm than good. Most newbies assume they are limited to those servers, and freeze deciding what box they should be in (or rightfully reject the idea of any boxes).
Tom EttyMastodon itself has only set up a few _general_ instances.
The other ones you see are founded and run by individuals or other organizations. Small communities have been built around these interests or identities. They chose this for themselves, so it can't be artificial.
Mastodon-the-non-profit has made a selection of these instances to showcase the wider community at sign-up, but had no hand in their creation.