Answer:
Different family roles and responsibilities between women and men
Step-by-step explanation:
I would say that different family roles and responsabilities is the most important factor, with discrimination against women by companies coming to a close second.
The reason is that many women have to interrupt their careers, often at very productive points in time, because of maternity and marriage.
Some of women when they get married, are expected to stay home by their husbands, and as result, they leave their jobs either permanently, or for a significant amount of time.
Other women, when they get pregnant and give birth, either decide by their own will to stay home with the child for a few years, or are expected to do so.
This career interruptions prevent women from reaching the top of the corporate ladder.