That preference is for the most part a social construct that is further reinforced by the salary gap between men and women. By encouraging couples to split pare

That preference is for the most part a social construct that is further reinforced by the salary gap between men and women. By encouraging couples to split parental leave equally, you lessen the hiring discrimination against women in child-bearing age, which in turn lessens couples' preference for letting the least-paid parent take the most parental leave, and thus you have a positive spiral leading to more gender equality.