I suspect that porn is a lot like Free2Play videogames, where almost everyone pays nothing but production costs and budgets are covered by maybe less than 5% of users that actually pay. But those 5% of users spend so much ridiculous money that it makes the entire venture worthwhile.
That said, I imagine that plenty of people pay for porn. People with particular fetishes that are underserved by streaming sites, people that waat high-quality or HD video, people that don't want to sit around waiting for particular scenes to be uploaded to a torrent service. People that are looking for a particularly obscure actress who only has a couple scenes on streaming sites but many more scenes on paysites. If you view porn as a commodity and don't care about video quality or a particular actress or a particularly good style of direction, then you'll never pay. If you can't find what you want for free, you just move on to something else that's not as good.
Plus since the death of Empornium and then PureTNA and then Cheggit, it seems like there's a vacuum in the porn torrent world that has left a lot of people wanting. There's no real central depository for all the pirated material, so I assume some enthusiasts just end up paying because they cannot find what they want on the dozen minor torrent/streaming websites that are trying to fill the void.