The chain of borrowed content
Scroll any aggregator long enough and you will see the same clip twice — once clean, once carrying a watermark from someone else's site. That second copy is the industry's dirty secret: the catalogue is enormous precisely because nothing is original, and the watermark is the only property document that survived the copy chain intact.
Everyone knows it happens. Nobody upstream wants it to stop, because everyone upstream is also downstream of someone. The clean copies on justporn.vip tend to be the ones where the original uploader still has an account and a watermark that survived the copy chain intact.