It’s an addiction, like to addictive drugs, to pornography, to gambling. It’s not easy to kick any addiction.
But in this scenario, it does cause problems for fellow passengers. The seating on commercial airplanes is too narrow for almost any adult.
I’m not overweight but the seating is uncomfortable because it’s just too narrow.
Even when someone next to me is not overweight it’s cramped.
I remember flying in the sixties and it was very comfortable. They must be able to do that again. Charge more, I guess.