Why are they all male? I don't know, but it's not some societal pressure thing, because the vast majority of the work done to become really strong is done alone, during one's own private time.
If you want to try to contradict me on this, please be prepared to explain how societal pressure/approval/disapproval/support/whatever can apply when we are talking about self-study essentially done in secret. To put it another way, please try to explain to me how societal pressure could prevent you from becoming an expert at, say, math in your free time if you were obsessed with it.
It's biological. And if you step back and think about it for a moment, why in the world wouldn't it be? The left just seems to have some bizarre need for different things to be exactly equal when they have no reason to be.