Some points of discussion are (unrelated to article):
1. If women were 25% cheaper than men while being as competent, wouldn't white/male capitalists trip over themselves to only hire women to increase their profits?
2. Women are less likely to negotiate salary and assert themselves, as women in general are more agreeable than men. Is this behavior based in biology or is it social construct?
3. Women tend to choose lower paying jobs, such as teacher, caregiver etc. In general women tend to care about people, while men care about things (STEM). Again: biology or social construct?
For example in Sweden, which is doing it's best to increase gender equality, sex differences between men and women maximized http://jamda.ub.gu.se/bitstream/1/833/1/scb_eng_2014.pdf
So perhaps occupation differences are healthy and natural. Of course, in Sweden engineers don't earn 300% more than teachers, so it's not a huge problem like in the USA.
The logical solution would be to increase pay in women dominated professions. But this kind of thing spits in the face of capitalism.
It's a tough problem to solve, and I still have no idea how to go about solving it.
EDIT: Additional explanations