When it comes to certain math- and science-related jobs, substantial numbers of women - highly qualified for the work - stay out of those careers because they would simply rather do something else.
Poor Larry Summers lost his job as President of Harvard for saying something very like this. One of the interesting findings was this:
That men, relative to women, prefer to work with inorganic materials; women, in general, prefer to work with organic or living things. This gender disparity was apparent very early in life, and it continued to hold steady over the course of the participants' careers.