There are plenty of NSFW oriented apps, especially in the AI category.
> It's popular with women and basically invisible to men.
Mostly true, and this might be a reflection of reality, but certainly not a justification.
And being long-form written text, likely invisible to minors as well.
It's extremely visible to teenagers. They're one of the main audiences for booktok.
> I also wonder why smut literature (the best selling category of books on Amazon) seems to get a free pass.
It's popular with women and basically invisible to men.