>>212075078 (OP)Not all fat people are. Well, to be entirely fair, extremely few aren't, but they do exist. Sumo wrestles for example are all excellent athletes, and they actually work hard and eat harder to maintain their weight.
As for why, it's probably to do with the perception that over indulgence and hedonism are distasteful, and fatties are almost the impersonification of those vices. Getting rid of extra weight is really fucking simple, just stop eating. But they can't even do that. Pathetic is what it is.