Many guys see relationships with women as a zero-sum game: If she wins, he loses. Marriage is the ultimate contest: Her job is to get him to capitulate to marriage. So many men see marriage as the "end of freedom," the end of boyhood. That's why bachelor parties are supposed to revel in that boyish irresponsibility "one last time." So many guys figure, "Why rush into something that means basically that you'll be a prisoner forever?"
I myself have participated in girl-on-girl shows for men that would ask for it, of which were very, very many. It is a popular request, especially at bachelor parties. It also paid a much higher dividend. Also when I worked the escort services, certain male/female clients would call and ask for a male/male team and the escort services that I worked for provided this specific request.