I don't go on Only Fans and have limited knowledge of how it works really, but I've got friends who do pay for subscriptions and they say it's down to the personalisation aspects of it. You can pay a bit extra for something really specific, you can contact the models if you want, that sort of thing. If you get off on watching a girl lathering herself with whipped cream while cleaning windows dressed as a slutty football referee, then you can work out a price and she'll do it. As much as there's a probably a porn video of everything in the world you could think of, if your tastes aren't exactly conventional it can be difficult to find the specific thing you're after. Pay a model £50 and she'll do it.