That's a separate issue that we (meaning humanity, not just America) is still dealing with.

During the second world war chemists figured out how to make cheap fertilizers and pesticides from petroleum. These two innovations shot farm productivity through the roof. Food became more abundant than ever before and therefore became incredibly cheap. Virtually overnight the biggest challenge to people's diets was having too much, not too little.

For the first generation or two living in this historic abundance, they had no way of seeing the coming health threats. Coming off of literally the entire history of life on this planet having too little to eat instead of too much, they weren't with a "more is more" approach. Cost of ingredients was no longer a barrier to adding more sugar, more salt, and more fat. At least in the US, there was a brief "convenience" fad in cuisine in the 11950s, but gears quickly shifted to increasing portion size and improving taste by the brute force addition of more salt and sugar.