The problem is explicit content requires escalation to keep an audience. They have to be able to one-up themselves by making each new thing they do more """exciting""" than the last, because the coomer demographic aren't particularly loyal and will quickly move on to the next thing that makes them feel good downstairs if the current one's getting stale.
Pornstars don't do anal on their first shoot for a reason. It's common practice in the adult industry to start off fairly tame, and keep more degrading and taboo material in their back pocket to generate a second wave of interest when their career starts to dip.