It’s not porn… it’s adult themed erotica. Huge difference! </sarcasm>
Posting your stories to other websites is fine, other authors do that. What they don’t like here are plagerists, spammers, under aged wizards, and things mentioned in the ToS. Look at the warning tags, the only subject topics actually forbidden are real-people-under-18 and where the original author has explicitly stated “no fanfiction allowed”. That, alone, causes some self-appointed morality warriors to have problems, therefore, the staff/moderators here have to be very diligent in enforcing those ToS. ( DG/BW/etc can give you tales of what they’ve had to put up with.) Every fanfic/story website I’ve examined, when I look at their ToS, are generally more restrictive than AFF when it comes to content.
DG/BW, correct me if I’m wrong, I think you can put links in your profile to the other websites, which can help them sort out what’s legitimate if they ever get a complaint about a possible dupe.