Gender Roles and socialization of males and females in Asian cultures might be the strongest reason. I recently conducted a study exploring gender differences in cognitive ability and was quite surprised to see that the differences only sustained when I was working with traditionally stereotype threat laden gendered fields. The gender differences turned non-significant when I was working with women from medical universities (in this case stereotype threats are not relevant).
"... In the centuries after Confucius, it became common for writers to discuss gender in terms of yin and yang. Women were yin, men were yang. Yin was soft, yielding, receptive, passive, reflective, and tranquil, whereas yang was hard, active, assertive, and dominating. Day and night, winter and summer, birth and death, indeed all natural processes occur though processes of interaction of yin and yang. Conceptualizing the differences between men and women in terms of yin and yang stresses that these differences are part of the natural order of the universe, not part of the social institutions artificially created by human beings. In yin yang theory the two forces complement each other but not in strictly equal ways. The natural relationship between yin and yang is the reason that men lead and women follow..."