1. Women earn less in most sports including chess because less people are interested in e.g. women's chess than men's. Men's chess generate more profit.
2. Why are they separate? I guess it's because women are statistically about 200 ELO lower than men. Correct me if I'm wrong.
By saying this you are directly inferring that Men are better at chess than Women.
If this is the reason why they are seperate, it shouldn't be.
I agree, there should be separate categories for men and women. There is a great video about this, I'll share the link. I think it's fair but not afraid to look at facts.
https://www.youtube.com/watch?v=arWdJiqwNI0