I think this probably doesn't need to be said but LGBTQ people on Mastodon are not an example of what I meant. To make it extra clear, I also didn't mean to imply that just any group with a strong presence on such networks is automatically "fringe" or worse...

It's just by my (admittedly subjective) impression large-scale, community-wide adoption of decentralized networks has been mostly by radicals or militants, because they have increasingly been banned from mainstream social nets. They had an easier time taking the hit from jumping to a new network, because they had been ostracized.