A common hypothesis is that there are genetic and social/economic aspects that push people towards one field or another. If you make an effort to remove all social forces, and succeed, then the only forces left are the inborn ones- so their effects maximize. So, if there are any inborn differences in the distribution of interest in e.g. engineering between men and women, you would expect to see their effects most keenly in the most low-pressure countries. Inegalitarianism adds pressure that money is useful for dealing with.