The gender division is because women on average are worse than men at chess and likely to be eliminated in a tournament early on if they manage to qualify at all.
This is because chess is a boys club where men and boys get better training and have an easier time advancing and practicing then women.
The best way to get better at chess however are tournaments, where you can play your equal under a stressful and emotional context. Since women can't advance as well as men because of discrimination, they wouldnt be able to play tournaments making it even more difficult to advance their game.
The women's league are created so that women can play in tournaments, get practice, get better and be able to play in the big boy tournaments as well as a creating an environment where sexual harrasment, which is also a problem at the main tournaments, is mitigated.
Edit TL;DR women's league are there because women chess players typically get sidelined. Its basically affirmative action.
More like "Republicans talking about Trans people like Nazis talking about Trans people"
The first of the famous nazi book burnings were targeted at an institute studying and trying to understand trans people.
https://en.wikipedia.org/wiki/Institut_f%C3%BCr_Sexualwissenschaft