I'm just thinking about this massage/sex analogy. It's an obvious thought, because prostitutes often advertise massage. I'm thinking on screen here ...
If you went for a massage, and the practitioner made it obvious they were getting a kick out of it, you'd grab your towel and run, wouldn't you? Then you'd make a strong complaint about their unprofessionalism.
When people go to a prostitute, they expect the practitioner to fake pleasure to the point of orgasm. They might even complain of unprofessionalism if this wasn't done. So they are paying for the pretence of shared intimacy, as much as (or more than) the physical experience. It's so NOT like going for a massage, it's practically the inverse.
Isn't this, too, why we use the term "prostituting oneself" for professional tasks that involve creating false friendships, as in some sales situations and political lobbying? When we're paid to pretend we really like people we find obnoxious, we feel the job's demanding a little too much of us and we'd better get a bloody good bonus for this one ... because intimacy, even without sex, is too important to sell.
Actually I did a lot of that in my career. After leaving the field, it did take some heavy readjustment to stop feeling everyday relationships must have an 'angle'. When I meet people now, I'm totally free to choose how I interact with them. I kind of get how this could also extend to sexual relationships.