What is the biggest cause of obesity?

No one’s gonna say but I’m gonna say it : lack of self-control. Obviously there’s poor diet , inactivity, genetics etc. But I’ve met skinny people with a horrible diet that were sedentary but their portions were small . Instead of eating 5 fried chicken pieces they would eat just 1 or 2. I’m sure there are other factors but I think that’s the main one.