We need to start looking at obesity as a hunger disorder, and not as the result of an addiction, a lack of knowledge about nutrition, or a lack of self control.
When an obese person regulates their eating and loses weight, the hunger often doesn't go away - and often increases. This is physical, not psychological hunger. When the obese person almost inevitably returns to eating to fullness, they regain weight.
When a person takes GLP-1s, hunger is greatly reduced, and an obese person can eat less food while still achieving satiety without gaining weight. When they stop taking the GLP-1s, the hunger returns, and when they return to eating to fullness, they regain weight.
Similarly, when a person takes stimulant weight loss medication, they can eat less food while experiencing less hunger, and thus lose weight. Similarly, when they go off of the stimulant (or develop a tolerance), the hunger returns and when they return to eating to fullness, they regain weight.
In many obese people, the hunger is present even when they eat a nutritious meal at the appropriate number of calories to maintain their weight. Common advice is to say "this mix of macros or foods makes me satisfied!" and, well, that's great for you but not universal.
People who naturally feel reasonably satisfied with an appropriate number of calories to maintain their weight still experience hunger, but not with the intensity or insatiability of that hunger that many obese people do.
While it does occur with some who have severe eating disorders, most obese people do not overeat themselves into obesity by continuing to eat long after they're full. They eat until the hunger goes away.
It's the hunger. Take away the hunger, and the weight goes down. Bring back the hunger and the weight goes up. It's simple, it's obvious, and few say it.