What's the percentage? 12% in Hollywood? How long did it take women to become doctors? lawyers? executives? Do you remember women's role in the 50s? Mostly supporative positions. Hollywood is just one of the few remaining places that needs adjustments.
I think the main reason is, men have spent too many years tuning out all those directions from the women in their life...
Sorry, no more sexist jokes. On a serious side though, it migt be because the male viewers don't want soft, frilly covers on their action scenes. But then you look at channels like Lifetime, Oxygen, and the rest of those that cater to the softer side, and I bet you find a majority of female directors- for the same reasons- women don't want their romances to be greasy, sweaty, and involving car chases and explosions.
As a woman I agree that part of it has to do with the lack of participation in school. I am not saying it's this is main reason but it does take part.
Girls (and I say girls on purpose) get intimated when put in a group to work on a film project because the men take over. It take a passionate woman to stand up for her creativity but that is hard to find in high school when you just want the boys to like you, yada yada. I myself was one of two girls in my film class of twenty in high school. The odd against our ideas were intimidating. I was fortunate enough to go to a college were individual projects was the norm and I could expand creativity freely.
I am also not suggesting segregating classes either because women need to be able to work with men to make it. That's just my thought to a part of the problem and unfortunately I don't have a solid answer.