Deliciousness and oversized portions are not, in fact, mutually exclusive
True, but if you can have both, why not? You don’t have to eat a whole combo yourself, my SO and I usually share an order of fries, don’t get sodas, and get our own burgers. If we go to a sit down restaurant, we’ll usually share an entre and maybe order an extra side if we don’t think it’s enough.
The real issue is that in American food they are much more willing to throw out the idea that food should be healthy and nutritious for profit and quantity.
It’s more that the restaurant industry is so big and specialized over here that if you want to eat healthy there are establishments for that, and if you want OP’s experience there are others for that. If you want the freshest, healthiest menus with scratch-made dishes you patronize local businesses. If you want the name brand dishes—most which are precooked and reheated—you go to one of the nationwide chains.