It's probably not the main reason why, but if you think about it, when a male gets rejected THEY probably think their peers think of them as unattractive, and weak in the sense that they can't pair themselves up with a woman. When women get rejected however, their woman friends are much more supportive. Not saying that male friends can't be supportive, i just think that there's kind of more not-really-there- shame/disappointment to be felt when rejected if you are a male.
And of course we have the whole "males can't express themselves as much." Which I've found true so far, i know a couple of very expressive male individuals, but the female count surpasses it easily.
Fear of rejection, fear of putting what you want in the hands of someone else.