It's just a theory of mine, but I think it's because it's easier to convey a scene within just a few panels than with photography, which require more effort to convey what it exactly is about.

Anyone can just create a porn instance, so why not as long as it's moderated (and hopefully not full of illegal content)?

There goes my Reddit addiction

a lot of specific nsfw communities are only for porn of women :(

The community doesn't seem to load for me on lemmynsfw.com, which is weird since other communities from kbin are able to load just fine.