The vitamins they use in supplementing breakfast cereals are the cheapest form available, and they have limited bioavailability.
That’s partly true, but when compared to all other food groups, they typically have log orders more nutrients than even raw fruits and vegetables. The only other foods that come close are frozen entrees, but those tend to be loaded with salt. Besides, no kid is going to eat 10 servings of carrots, squash, or kale for breakfast, but they will eat one serving of cereal. I’m sure there are plenty of kids in the world who would be much healthier if they had access to breakfast cereals.