that relies on many small vendors and one big vendor
It's hard to run your own porn business even if you are a major company.
People act extremely sensitive about their fetishes and think they are connoisseurs. but the reality is that 1000 porn movies in the 70s and 80s could satisfy jackoff habits of the whole global population for the forseeble future.
The marginal value of more porn being produced is essentially zero
OnlyFans is very present in culture and has a monstre evaluation, but if you look at revenues you'd be looking at the sum of some 300 big gas stations. Also OF is not a porn website it's an online GFE service.
99% of everything is crap. Most new movies or books are awful or entirely pedestrian and completely unoriginal to boot, and most don’t turn much of a profit.
But people still make them for a huge variety of reasons.