I generally agree with you but I don’t think you are taking into account individual nutrition. For a fat person to lose weight they need to eat less. When this happens your body literally screams at you not to. This doesn’t end when you are no longer fat. It is a constant battle and your body is constantly trying to reach the fat state again. Unfortunately when you restrict your diet to lose weight, or keep it off, this itself can cause deficiencies and malnourishment.
This is very much a systemic issue but it is also tied into culture and personal responsibility. Unfortunately it is very complicated and not the same for everyone.