I think it's a bit more popular outside the US than you make it out to be. As an anecdote, I know a handful of people on it in Denmark - and that's despite the local Danish price being higher than the German one and Denmark having notably lower obesity and diabetes rates than Germany.

I imagine you'll find that people of certain lifestyles tend to cluster together a bit, with those with more active lifestyles and healthy diets likely to have their friends and family be of active lifestyles and healthy diets, and in turn less likely to be in need of such drugs. Lifestyle changes are difficult to implement by nature.

Although, the term "processed food" is awful as it covers so many unrelated things. The problem is ultra-addictive, ultra-high glycemic index foods consumed in large amounts partly due to their addictive qualities - a quality some processed foods have.

For reference, Danish sausage sandwich toppings are highly processed foods, but it won't drive anyone to obesity or diabetes. Elevated blood pressure, perhaps. Junk takeaway, candy and sugary cereals on the other hand...