Lemmy actually has two different "trending" feeds. Active, which seems to show posts that are getting more comments, and Hot, which seems more focused on votes. You probably have Active selected by default. Turns out porn gets lots of upvotes but doesn't generate a lot of conversation.

[–] smeenz@lemmy.nz 1 points 2 years ago* (last edited 2 years ago)

I've just checked both active and hot (and for what it's with, also checked new and and the other options). No porn or nsfw posits in at least the first several screenfulls of scrolling through "all"

Show nsfw is turned on on my account settings.