Guys are good at doing one thing and concentrating on it really hardcore and stuff, if they loose interest they loose interest pretty majorly, however you get those awesome guitarists that never lost interest.
Girls multitask so they're used to doing loads of different things, so i've never seen a girl stay at home and play scales and songs instead of go out with friends or do something else, guitar is like a fraction of a girls life imo, guitar is about all of my life (apart from say the gym, but that's more like maintenance).
That's just imo, there are always the exceptions. and perhaps it is a society expectation thing, but imo it is a biological thing too.