I don't think it is the managers who want to take the risk.  But as long as more women take the full year parentally leave than men, they take themselves off the ladder for a year and end up behind.  Even as a male I have had this happen.
It is time we debunk the myth that the wage gap is do to discrimination.  Even in occupations where men and women have fixed pay structures, such as family physicians, men tend to make more than women because they work longer hours.  
While women now out number men in university, they tend to congregate in social sciences and humanities, which, for both sexes, do not pay as much as the STEM occupations.  
There is one area of STEM that is dominated by women; veterinarian sciences.  This clearly demonstrates that there are no barriers women entering these programs.  In fact, women are not looking after the cutesy animals like teacup poodles and the like, but are heading more and more into large animal practices proving their abilities..