That's conjecture though and no conclusion can be drawn from what is simply a statistical analysis of weight loss other than, as someone above said, society weight loss strategies should be changed.
Prevention shouldn't be the goal though, we need to change the entire food industry to help support healthy eating.
I think it's reasonable to infer that "willpower" in cases like this are mostly an illusion. I absolutely agree with cagey for a
scientific paper, but for lay observation it is absolutely reasonable to assume that most people don't like being fat. There is tremendous pressure on obese people to lose weight from a variety of angles; their doctors will tell them to lose weight, and everyone is aware that being fat means you are likely to die younger. There is social pressure, as nearly everyone is aware (consciously or not) that fat people are given lower social status than skinny people. In some cases (especially children), obese people are openly mocked and ridiculed. Romantic options are fewer, too. And of course, there is internal pressure, as obese people often have lower energy or chronic pain which can be readily managed by being skinnier.
If we have statistical analysis which shows that people remain obese even with this tremendous social, medical, romantic and personal pressure to be skinnier, then that suggests it's not meaningfully in people's control. If it was, fewer people would be obese.
