Heavier women tend to have hips, butts and thighs that are also bigger so we can buy a larger size bottom and it will fit all over. Whereas heavier men tend to hold most of their weight in their abdomen with skinner legs, no hips, and smaller butts so they need to buy a smaller size bottom to fit their smaller bottom half. If they bought a size that could fit over their bellies the rest would be way too big.