Because it pisses off a certain demographic who can't handle anyone with curves, let alone ones on an extremely cartoonish body. And pissing people off like that is fun and goes to show how insane some people really are.
Besides that though, some people just actually like it because fuck you some people just have different taste. They like the cartoonish exaggeration, and there is literally nothing wrong with that.
Some people prefer more realistic proportions and that's ok too, nothing wrong with that.
Just stop being such puritan fuckwad already.