It's because of the chivalrous ideal of the perfect gentlemen defending women. As it so happens, that is a legitimate concept. The problem is not that men are exhorted to protect women, it's that women won't shut up and let the man protect them instead of acting like backseat drivers.

This is the great error of mainstream conservatism, they see men are abandoning their chivalrous role and decide the problem is men instead of focusing on the women that completely abdicated and even attempt to subvert their end of the bargain.