The demand is created by human beings too inadequate to create natural, mutual relationship(s) to satisfy their needs, and/or masturbate, and/or control a sexual need for a period of time.

I'm unconvinced that sex is the only dynamic.  Somewhere when researching this I found the claim that the 'typical' client is 35-55 years old and has, or has had, a wife or girlfriend.

As a student, I lived on the edge of the red light district, and my own impression was that the typical kerb-crawler is 35, normal looking and in a company car.

I don't think prostitutes are the only option for sex for these men.  Which means that they must be paying for something else.