Thinking about it some more I bet part of the appeal is the voyeuristic nature of it. It probably feels a lot more like real life, where you very rarely get jumped by horny housewives looking for an anonymous lay, and more realistically get some sideboob or a panty flash from people wearing hot weather clothes.

But as you note, it's mostly a good deal for the producers that can monetize the videos a lot easier on a legit platform like YouTube, and there is probably a reasonably big captive market of people who are trapped behind porn filters.