Because that's what the research found. I'm not assuming anything - I'm passing along what studies of this topic indicate.
"Women initiate divorce 69% of the time and what these women report when choosing to leave a marriage and a man that they might still love are all of the things discussed above: Emotional and sexual disconnection, feeling taken for granted, a man who doesn’t make maintaining the relationship a priority in the same way that they do and who doesn’t do his fair share at home.
Rosenfeld said his results support the feminist assertion that some women experience heterosexual marriage as oppressive or uncomfortable. “I think that marriage as an institution has been a little bit slow to catch up with expectations for gender equality,” Rosenfeld said. “Wives still take their husbands’ surnames, and are sometimes pressured to do so. Husbands still expect their wives to do the bulk of the housework and the bulk of the childcare."
