25% is the number you were looking for, and even within that group I think you'd find plenty of people with a healthy BMI that are in fact not living a healthy lifestyle.
I think it's a lot simpler than that. US has an abusive relationship with junk/processed food. It's so deeply ingrained due to profit margins, wealth inequities, nonsensical subsidies, etc. that the only feasible solution is to introduce a drug that continues to allow that relationship to continue.
It's a lot easier of a solution than it is to tell companies to stop making garbage or saturating everything with sugar and HFCS. "Easier to see end of the world than end to capitalism" -- its the same shit packaged in a different story... Easier to introduce a drug to treat the symptoms than to solve the actual problem.
Mind you, I'm not implying that it is easy. We have collectively accepted this which makes change difficult if not impossible.