As a foodie in the US and one of the older members here that still has a decent physique, I'll just say it boils down to choices and habits.
Like already stated, processed, premade, and fast food made by corporations that care only about profit, fill these foods with everything that will make them taste good and sell. (salt, sugar, oils, artificial flavorings & preservatives) Living in a city known for having an agenda against fast food franchises it's been easy to eat out at independent restaurants that have to care about the quality & integrity of their product. I have a weakness for a good cheesesteak and fried chicken every once in a while but I don't weigh a ton cause I don't frequent KFC or BurgerKing/MC'D and go to reputable local shops instead. Otherwise I'll make my own food, plus I'm a fisherman that catches my own seafood, a large part of my diet.
As for habits, much of USA is sedentary watching too much TV & video gaming and consuming these toxic foods, and seeing more advertising of them, so it becomes a vicious cycle. I don't do vid games, watch little TV, and spend most of my time playing music, fishing, women, and it paid off, especially as I'm getting older being active has really helped.
We all have these choices, grab some fast food, a frozen dinner, or take the time to cook (or learn how). Watch your favorite TV show, play the latest video game after a meal, or do something active. Makes all the difference in the world.
OP there are some good points you make but don't kid yourself about some of these things or come to false conclusions.
- Losing weight while on vacation is actually fairly common as you tend to be more active doings things while there, and traveling itself burns calories. Not to mention if you visit somewhere with a warm climate that encourages sweating and burning fat.
- RE:Baklava - I'm Greek, have made it many times, and it's actually mostly nuts and phyllo with a sugar/honey syrup. Nowhere close to being as fattening as something like ice cream or fast food.