How do you know this? Have you done things like looked at research indicating the causal links between gut bacteria and obesity? There has been a surprising amount of it, for a random example https://www.sciencenews.org/article/obesity%E2%80%99s-weight....

I see no reason to believe that having a struggle to control weight is any more under our control than a desire to have sex with members of our own gender. Our conscious has influence on whether we actually do so. But some people have no problem, some people can struggle and avoid a problem, and some are pretty much doomed.

Note that I'm not arguing about whether we "struggle with" weight control or not. Some people absolutely do feel hungrier than others while maintaining the same daily energy balance. But the choice of how to handle that hunger, to keep overeating when you know you are already overweight, or to stop eating even though you still feel hungry, absolutely is something that an individual can control.

   indicating the causal links between

What reason do we have to believe that questions of free will are transferable from the mouse model to humans?

Citation needed.

In fact there's a HUGE industry of obese people making the choice to lose weight (diet, gyms, etc) and failing.

There are effective weight loss coaches but since you already know their advice (which is that you need to permanently commit to regular exercise and you need to take permanent control your energy balance in order to sustain a target weight), and since their advice requires discipline to follow, they're somehow not as popular.

Several studies have shown that we're not good in discipline at all, unless for people that it's innate. So discipline might be a factor out of our control too (genetic), and it's just the presence of people with more innate discipline (against genetic) that makes it achievable.