Honestly I think it’s a lot of things.
First, guys are not typically good at thinking with their brains when sexually aroused and there is a willing partner actively trying to talk you into it.
Second, straight guys tend to wind up with people assuming they are gay if they turn down sex. I know officially it’s not supposed to be a big deal, but do you really believe that teenage boys call each other “faggot” for it to be a compliment?
Ultimately I think boys see less of an impressed risk factor with sex. Sex by men is still seen as an accomplishment. Even if you aren’t in the mood you want to be seen as successful by other guys. The media is a contributor here. You see romantic comedies about teenage boys tried to have sex (American Pie, etc…). Can you imagine a series of movies about sex crazed teenage girls trying to talk their boyfriends into having sex with them?