There should be a kind of “sorting hat” personality test to attract the interest of prospective Lemmy joiners. People who love solarpunk stuff, for example, would easily find their home in slrpnk.net. Set a link to it on sites like join-lemmy.org to make the fediverse more approachable to casuals.
Many (most?) instances do block porn. Aside from liability concerns, porn tends to be high bandwidth, meaning high costs to operate. As such, there are a handful of VERY NSFW instances that aren’t well-federated.
Of course, it depends on how you define porn. I see a ton of suggestive (but not outright pornographic) anime when I browse All/New, but very little of actual naked humans.
I totally understand why they would do it. I don’t understand why or how they block the NSFW instances without them appearing in the list of blocked instances.