I don't know why but people seem to have an obsession with "taste" even to their own detriment. Every time I see submissions on HN about artificial meat in the top 10 comments you can find multiple people talk how this is great and how companies can use this to increase the flavor of the meat.
For companies that need to make a profit increasing flavor generally means adding additional ingredients or processing the food in a way that is as cheap as possible. Often this means adding high fructose corn syrup, sugar, carbohydrates or fat far beyond what is naturally available in the food.
Instant Ramen is an extreme example of this. Instead of just drying the noodles they deep fry them because it is cheaper and fatty foods "taste" better. Suddenly noodles made out of flour and water which should have zero fat now have 25% of their weight as fat in addition to the existing carbohydrates. I'm sure you can find less extreme examples but across the board this could result in x% more calories being consumed even if people eat the same things they did 30 years ago.