Why do girls and women of above average size get made fun of?

I know someone that is 5’11, large built and about……I’m not telling you her weight. No woman wants to tell people that. Let’s just say she isn’t slim. Anyways some guys pick on her and tease her about being a “big” girl and not a lot of females are that big. I mean it is true but it isn’t cool to do that. She is very insecure because of her size and her big feet when people point it out. She wishes she was average size or petite. Her dad and mom reminds her that she is above average and she won’t wear the stuff average ladies can wear and they have to look at certain places because her clothes size will cost more. Her friends teased her for being “expensive”.