It's a little hard to explain something like this, but I'll give it a shot since I'm a male.

Men are attracted to long, soft, silky hair on a woman, right? It is one of the many things that we look for on a beautiful woman. Long hair is something that we desire (sexually, romantically, etc.) to touch, feel, etc. Now when you take something that is so desirable on a female and put it on a male, it kind of taints it and makes you feel uncomfortable. It kind of makes you feel like you're going to start becoming attracted to guys now since they have something that you desire on a woman. I mean no heterosexual male wants to see ample breasts, shapely legs, or a tight ass on a woman, right? I'm sure no heterosexual woman would want to see breasts on a guy. Plus, I know I wouldn't want to see facial hair or chest hair on a woman.

My point is that long hair on a woman is something that us males cherish and feel it makes women unique. When you take something so special and desirable and put it on a guy, it just feels weird and it's like combining two things that normally don't make sense together (like military intelligence :P). Us males have a romantic and sexual desire when it comes to long hair and when you take long hair and put it on a guy, it's just uncomfortable.