One explanation is once you're free to do whatever you want and you don't have to worry about expectations or putting food on the table so much, the influence of subtle innate genetic preferences actually become much more apparent in some ways.
However, this explanation goes against the rules of the western view that predominates, that the gender ratio of fewer women in some area (but often not when there are fewer men in some area) mean is proof in point that women are being harmed and should be given assistance.
If discrimination causes the difference, why do countries like Iran or Saudi Arabia have around the highest ratios of female engineers and countries like the Netherlands or Norway around the lowest?