Shitty moderation, which is an issue with the startrek.website instance as a whole. RootBeerGuy provided the gist in a comment below, but the catalyst for the exodus was when the mod deleted a post about Sarah Silverman making out with Tuvok. I mean, it sounds lame, but Risa was supposed to be a shitpost community, with its sole rule being "there are no rules". It was supposed to be a fun place. It happened a few too many times, so the top posters created the tenforward community here on lemmy.world.
A lot of people followed, and within 48 hours the activity on Risa dropped down to almost nothing. The handful of stuff that is being posted is cringy boomer humor.
This is now a very subjective opinion that I am not backing up in any way, so take it with a grain of salt:
Thats not just Risa, it is the whole instance and its moderation. Especially during the first months I had seen some really weird decisions in the startrek community on topics or comments that got deleted.
It is the reason I started making accounts on other instances because I dislike the complete non-transparency about that. Comments or topics asking about those deletions were gasp also deleted.
So whatever, glad people moved away. I am quite dissapointed that a whole instance based on one of the historically most inclusive sci fi shows turns out to be not so all embracing.
Edit: I should clarify, the events I refer to were nothing about anything lgtbq+ related. It was, in my opinion, harmless discussions or mild jokes about some posts. No terrible trolling or shitposting. And then when people asked about where that post went, those questions got deleted too. So it is nothing too scandalous and I would not think anyone needs to care greatly about it. But it showed to me that I disagree with moderation and it is probably wise for me not to have my main account on that instance.