Obesity isn't caused by bad diet. It's caused by overconsumption for a low effort lifestyle.
Even now, as an adult, I find weight management complex—I've been close to obesity while running up to 80 miles a week in marathon training, hitting a 3:02 marathon (6:58/mile pace). After finishing the marathon and cutting back to 40-50weekly mileage, my weight just naturally decreased. My appetite was much less when I wasn't running such high mileage. For me, it's a journey that seems to involve many factors beyond just low physical effort or overconsumption.
For many they wish the reason was as simple as them just being lazy, because then they would only need to tackle that one simple flaw. But it goes beyond having a lazy/sedentary lifestyle. Does it contribute? Absolutely, but there are examples of lazy/sedentary people who adopts an unhealthy diet and lifestyle who are on the opposite extreme in BMI. To treat the obesity epidemic in the States as an individual failing on all who find themselves in that category is to downplay the systemic failings that have allowed this to happen.
It's kind of weird how this is simply another avenue people take to put themselves on a "I'm better than you" pedestal.
That's what the orthorexic religion is really all about: Nobody should be held accountable for their decisions because of the other who did something bad to them. This belief system doesn't want people to seek real solutions to their issues because that reduces the size of the flock who can be marketed to.