Presumably these men cannot get enough for free. They may be happily married or partnered and enjoy regular and fulfilling sex - but not often enough. These men prefer bought sex to betrayal. Relationship sex, even with someone you love, can take time and be troublesome. Perhaps there's no time for a full performance - and she may not want an edited version.
Some men just are no good at turning on their partners.
You know the type. He pinches your nipples, gives your thigh a bit of a frantic rub and then asks if you are ready. Good-natured quickies on a week night are out of the question. It leaves intact the exclusive emotional bonds at the real epicentre of a relationship. However, for those men who like the thrill of the hunt, the gamesmanship of courting and conquest, the shock of the new, prostitution isn't the answer, more's the pity.