

I don’t know the full story but I’m aware of an association between pleroma and some of the nastier, nazier corners of the fedi. My guess is that many of the larger instances running pleroma have been defederated from their masto counterparts.
A quick Google of “pleroma Nazis” gave me this, probably more nuanced, explanation: https://medium.com/@Trevatos/gnu-social-pleroma-and-the-mastodon-culture-conflict-3b10872937c2
*porn involving some or all of the above