Because some people like to make themselves feel superior to others that are overweight or short. Usually shallow narrow minded people do these things. Real people don't care about those things. They care about a good personality, not looks.
Why do people treat you bad if you are an overweight person, especially a woman. What about the short, why are short people treated badly?
I think short people are just teased; it varies in rudeness, but I don't think anyone dislikes you for it.
I guess it comes down to media and influence.
Acceptable in our culture: Overweight mothers from having children. Men with small to medium large pot bellies.
Ridiculed in our culture: all children suffer scrutiny at some point, obese women- more than obese men, single overweight women, too skinny men
It's too bad we care so much about appearances, oh well
Also I feel like it's more acceptable for richer people to be overweight