If you're okay with second or third hand discussion, read on. Otherwise, ignore me. I block all the image and video based nsfw communities (well, almost all, the ones that are art based I keep in). So, grains of salt.
But, what I hear from people offline and online privately is that the fediverse is a disappointing place for spank banking. Too much junk, bad gifs, and hassles combined with spurts of spammish posts when a new community starts.
So even people otherwise engaged on the fediverse just don't bother you try and engage with lust here because it feels empty.
Hell, part of the reason I block them as they show up is that so many are just random porn gifs and stolen pics. Which is fine for what it is, I guess, but certainly nothing to engage with. You know damn good and well when that's the posts that most of the people posting just aren't going to have a good conversation. The gone wild style communities should be different (and I've heard they are, though too damn many onlyfans models that aren't there for the community, just the the free ad space it amounts to).
I dunno, there's also the way that lemmy in particular skews a little older and more settled. As people age up, the horny becomes less something to chat about and more something to actually participate in when one could be chatting. So you end up with a smaller segment of the user base that will do more than just vote and masturbate.
I suspect part of that is also the reddit exodus. Reddit was getting spam driven in terms of adult content, outside very niche (and often quarantined) subs.
In other words, people are still horny, but the fediverse just isn't the place to actively pursue it.