It's really not that simple. Starchy carbohydrates like wheat, corn, rice, and potatoes are, dollar-for-dollar, legitimately more calorie dense and more shelf-stable compared to healthier fruits and vegetables. They were staple crops for good reason long before the advent of modern agricultural subsidies. Salt is also very abundant, cheap, and not subsidized.

I do think agricultural subsidies are distorting the market and our food system, but eliminating them isn't going to magically fix everyone's diets overnight.