Fat women are so gross, they ruin the human race

Why did we evolve to have such a prominent lower body mass index in females? Women don't need to run away from predators, estivate, or migrate long distances like men do. They're usually safer than us and are often more stationary in terms of daily activities like being at a desk at work or school. There is no logical reason why women should have such a prominent role in food preparation and cooking in society. It just makes sense that thin women would be more beneficial to human survival than fat ones. Why did natural selection act like it saw no difference between male and female body proportions? Did it simply not matter? Or is it that natural selection is dead in the water since the rise of agriculture and we're all just waiting for the impendent singularity where health clinics and hospitals will be replaced by robots?