Losing weight isn't complicated. Eat less, move more. That's it.
Losing weight is extremely difficult. The drive to eat is a fundamental instinct. That instinct isn't calibrated for constant easy availability of food. We inherently want to eat more than is good for us in an environment of abundance. Fighting that requires a great deal of willpower, which is a limited resource.
Successful weight loss comes down to figuring out how to reduce your intake and increase your movement without requiring more willpower than you can actually muster. This is really hard. But losing weight is still simple.
You track your calories, you track your weight. If you're not losing weight you reduce your calories until you are. This method compensates for peoples differing metabolism and activity levels.
I can't find the exact study but here are two on the matter
I would suggest people are overweight because the steps to lose weight are unpleasant, or require willpower, rather than being too complicated and mysterious.