Lmao i have actually never heard of those websites except ao3. Yeonsu
You must be younger than am I. Back in early, early 2000s, fanfiction.net and adultfanfiction.net were the places to be for smut -- even original smut. Then ff.net cracked down on smut and aff.net stated getting wonky, so people moved to livejournal. Then AO3 was opened, and everyone flocked there.
Ngl the author must have read Wattpad as their bible.