i am in no way a sexist, but i do believe there is significant scientific evidence that shows that there are differences between men and women other than their genitals, and that some of these diffeneces come into play in racing.
i can think of two main factors.
first, males are generally better at spacial relations, ie, keeping track of their own position relative to other moving objects, and this comes from our evolution through the hunter/gatherer period. spearing a charging mammoth and racing towards T1 have a lot in common.
second, as noted by someone else already, males have more testosterone. it's a powerful mind alterning chemical that when combined with adrenaline makes us do stupid things that women will tend not to do. sometimes taking those stupid risks make us crash, but other times they pay off, and we win the race.
now, this is certainly not to say that women can't be good drivers, or that all men are better than women. the differences, while real, are still small, and there is variation among the population, so it would be quite natural for some women to be pretty good drivers, and some men to be pretty bad. but at the highest levels of competition, even a small advantage is an advantage, and so even if none of the social hurdles faced by women were there, they would still have a very difficult time competing.