Quelsen is correct in that everyone has their flaws, and obesity has multiple, complex causes. For some it's hormones. For some it can be depression or other mental health issues. For some it could habit - the way they were taught to eat growing up. For others a stressful life(or a life with other priorities besides being lean) could be a contributing factor. It may be different combinations of these from different people. Until people acknlowedge that any of the above can contribute to obesity/overeating, and that some may be present and others absent in different people, we're not going to solve obesity.
I believe jimhensen is also correct in that in the not-too-distant past when food availability was highly variable, overeating when food was abundantly available was actually a highly adaptive behavior, leading to better wellness and survival during times where food was scarce. However in the presence of quasi-unlimited food availability it's potentially maladaptive.
Obesity is a complex, multifactorial problem, period.