Females are judged negatively because they are naturally predisposed towards fecundity. When abundance of food was a sign of wealth, and therefore an indicator towards the provision of the expected children, the rotund woman was sexual. In the modern first world, all but the homeless can fatten themselves artificially on cheap sugars, so being fat is a negative and a sign of personal neglect regardless of the genetic and metabolic truths of the matter. No, we must have skinny girls, tending towards the smooth and prepubescent. I have not yet met a girl regardless of weight that did not wonder if they were fat.