The acting part is typically the enjoyment, or the setting (plumber fucks housewife etc), or the mere fact that the scene takes hours to film but results in 30 minutes of content, because the actor has to get hard, stay hard, get wet, stay wet, hold off orgasms etc, perform fake rough sex in some cases.

There's a ton of acting. This is why sexual abuse and rape is still a common industry issue, because the chemistry and enjoyment is usually an act, not real, and this can lead to consent being disregarded because of how vulnerable this form of acting can make someone.