The low number of female pilots is indeed somewhat puzzling. Airlines over here hire them for quite a while now and it is absolutely normal to have them doing that job. However of all applicants for cadet training with the airlines there are only around 5% female ones. Even if the airlines try to give them a slight advantage they do not get more than around 5 to 6% female applicants of all applicants that do pass the entry tests. The pass rate during flight training is then the same as for the male ones.
Funny enough with a very similar if not even more thorough entry test system there are around 50% of female ATCO applicants, both applying and passing the test.
Or simply said, most women are way too clever to even try the airline way, they rather take the better paid, stay at home job of an ATCO instead and fly in their spare time. Doesn't say much about us males on the other hand, we are apparently just waiting to get blinded by that stupid dream about flying the big jets.