Of course they've thought of it. They're not doing it because consistent dieting and exercise is a pain in the ass.
Dieting and exercise "don't work" for most people because most people STOP doing it after a while.
Aside from legit medical conditions, the reason people are fat is because they've decided they'd rather not do the work.
President Trump is obese by any definition. Are you saying he’s fat and you’re skinny because you’re a harder worker than him?