Not only are processed foods more readily available, usually less costly, they are also more CONVENIENT, and that is probably the most overlooked factor. Our society has only become even more fast paced and while the cost of living has soared, wages have basically stagnated since the 70s so people are working more just to bring home less. Imagine a parent; physically, emotionally, and mentally worn out having to feed a family. They are more likely to go for foods that only require them to heat, if that, or that their children can just put in the microwave, and prepare themselves.
The solution to this is multifaceted. We need to pay people more so they do not have to spend a disproportionate amount of time working, we need to incentivize producers of processed foods to actually prepare foods that are nutritious since people are going to continue to purchase them, we might as well work with them to better our health, than against them, we need to eradicate food deserts by incentivizing the development of grocery stores offering more nutritious items and farmers markers, and we need to bring back home economic classes, make them MANDATORY so that our children are taught how to make meals that are not only healthy, but tasty too. If food is healthy but not tasty, we will still struggle to get people to eat well.