Bodybuilding magazines are there for one thing, selling products. SInce the gay and bi population only represents a very small minority of the population, it would be very silly marketing to such a small audience. Your mainstream gym rats are the ones buying the majority of the products by number (protein, creatine, glutamine, vitamins). You would go broke just marketing to gay people. Almost everyone I know has at one time worked out and used some supplementation. Especially in highschool, and their 20's.
Sure there is a gay component to bodybuilding. You're talking about the most physically developed males in the world close to naked on stage. Some go the escort or posing route because bodybuilding is damn expensive and pays nothing unless you're near the top. It's easy money and some just can't say no.
Look at women's fitness. So many escort, perform porno, wrestle and pose. What is their target audience. Lesbians?
