It's actually a fairly complicated and can be quite difficult for people to break out of, even people who desperately want to change. When people follow the standard guidelines (which are beginning, slowly, to change) to avoid fat and reduce calories, they end up feeling hungry all the time, and have to white knuckle their way through. This is not a state that people can maintain long-term.
Starvation studies from the University of Minnesota have been described this way: "During the semi-starvation phase the changes were dramatic. Beyond the gaunt appearance of the men, there were significant decreases in their strength and stamina, body temperature, heart rate and sex drive. The psychological effects were significant as well. Hunger made the men obsessed with food. They would dream and fantasize about food, read and talk about food and savor the two meals a day they were given. They reported fatigue, irritability, depression and apathy. Interestingly, the men also reported decreases in mental ability, although mental testing of the men did not support this belief."
In addition, there is evidence that the body begins to reduce energy output in response to reduced energy input, thus making the advice every overweight person hears from nearly every source to "eat less and move more" a load of nonsense. That can work short-term, but the combination of reduced energy output and constant hunger make that recipe very ineffective long-term.
There is even more to complicate the story (e.g. it is common for overweight people to feel hungry even with massive amounts of energy stored in fat due to some of the effects of what's now being called variously, metabolic syndrome, syndrome X and diabesity).
In short, when people become overweight, which is a progressive condition of insulin resistance that grows slowly over time, or in other words and emergent hormonal dysfunction because of diet, they cannot "eat less and move more." To that extent it is not self-inflicted especially since millions of Americans are doing exactly that as told by their doctors and it is having no effect.
The only way to really change body composition long-term, is to change diet in a way that is at odds with what doctors learned twenty years ago in the two days they studied nutrition in medical school, which, as it turns out, is wrong.