I think the thing you have to take into account is that, atleast right now, game developers still focus their games towards a male audience. Thus, there is a path of reasoning that follows such as: a)since males make up a bigger percentage of the audience, it is assumed that they will choose a PC gender which mimics their own, and thus more people will choose to play as a male PC. Therefore given a), that would suggest that b)it makes more sense to have the main romantic involvement be the one to fall, and that entails making it the female NPC romance option that is the one who falls.
Given a) and b), then it would make very little sense to build the story around a male NPC who is the one who falls, since most (in terms of target market) gamers wouldn't really care as much if their PC's male "buddy" fell from grace. It's more of an impact if it's your PC's romance option.