Obese people acting like they can’t control it is precisely why they’re obese.

Body Mass Index doesn't do a good job of scaling by height. Its much easier to qualify as "obese" when you're 6' tall, simply because your frame is so much larger. And quite a few people really are just larger. Samoans are large folks, which is why they produce so many football linemen. South Americans tend to be a lot smaller and leaner by their nature.

You can change your diet to cut out the excess sugars and limit your carbs, but a person whose body demands 5000 calories a day is simply not going to be the same size as someone who can get by perfectly fine on less than 1500.