I've heard elsewhere that a big part of that was U.S. public sentiment turned strongly against fat, particularly saturated fat, in food, but people wanted the food to continue to taste good rather than take the 'taste hit' taking away the fat entailed. Upping carb. content was the resolution of that problem (and created more problems).The food industry uses sugar to replace healthy fats for more storage life and reduced cost. It is addictive and it helps sell more products.
Then they came out with indigestible carb.s as sugar-substitutes, and there is a lot of back-and-forth controversy over that (e.g.: Splenda, Aspartame).
While you could make a 'chicken and egg' argument over healthy food and consumer demand, it seems like if there was a strong consumer demands for healthier food, some company would be marketing product to meet that. We see some signs of this - such as food labeled organic, low-fat, no-added sugar (but check the carb.s on the label - food is a 'buyer beware' thing), etc.
Big companies don't necessarily have an agenda to make you fat; they have an agenda to make a lot of money by offering product we're willing to buy a lot of.
Case in point. Many years ago on a honeymoon cruise I was in the main dining room onboard and a waitstaff person brought about a basket of various types of bread. I think this was sort of 'European' style. I'm an American accustomed to O'Charley's hot, soft rolls with butter to smear on them; I'd heard of Europeans going on about their bread, so I eagerly tried a piece. Blech! It was like gnawing on cardboard.In many countries the commercially available bread is equivalent to what our ancestors would’ve called cake.
Before anybody starts in that freshly baked bread in some European bakery is doubtless way different than what I was offered on that cruise, I don't dispute that, but the idea rolls should be soft and hot seems to run afoul of some foreign preferences (did a little Googling to confirm that).
I suspect at least in some large cities there are businesses making European (yes, I know that's overly reductionistic) harder/denser breads served cold, but...they don't seem to be taking the market by storm. And if a lot of Americans wanted that, seems like they would be.