Weight is a technical problem. Eat less than you need and you lose weight. Eat more than you need and you gain weight. Simple.
Willpower to follow through with the technical steps to lose weight is a mental health issue. That is way more nuanced, complicated and ultimately why so many people can’t lose weight. I think you consider them holistically, whereas those who disagree with you keep those concepts separate. There is a logical argument for both and neither argument is wrong.