I think the open secret is that prostitutes don't count, because the sex isn't about having orgasms, but about having one's merit validated. They must earn the thing that they cannot buy. Sex is the ultimate compliment, being chosen by a woman who dubs him worthy -- ideally, the most desirable woman (as perceived by other men). And for many, the more the better -- a second time doesn't count as much.

They generally don't get that, and will give other reasons why they can't just hire somebody. But I believe that's the real reason: it's the one thing that they cannot buy, and therefore matters most when they have all the money in the world.