The issue at hand is that working women make considerably less money overall than working men. This is due to any number of factors including sexism, social effects, and the necessity of being present at, key, moments of the child rearing process. In the current iteration of our capitalist system it's required for nearly everyone to work, especially in the lower classes. Women have all the same needs that men have, and they have to cope in a society that, for many reasons, pays them 30% less.
Identifying those factors and working to minimize or eliminate their affect is a noble goal. But there are some factors that can't be eliminated, and we wouldn't want to live in a world where they were.
Feminists are right that there is a problem, this is a demonstrably unfair society. It doesn't matter what the reason is as much as it matters what the solution is. People spend a huge amount of time arguing about the problem, who's fault is it, what factors come into play.
I don't want to live in a world where women are men. Where they can't take time to start a family and properly care for their children, because keeping the money flowing is a more immediate need.
I want to live in a world where you can't just take time off to raise a child, but also to do art, or to travel, or to simply be a human who exists outside their office.
TLDR: Why matters very little, the income gap exists and we should fix it.