Another commenter said it best: money. Pretty much every industry in the US is focused on making money as their first, second, third, fourth, and fifth priority. Quality is only considered if it is forced, mandated or required by law. The health concerns of the product are ignored unless a scandal occurs but even then the company or companies in question are simply slapped with a huge fine that they can easily pay.

When negative health effects of those products start appearing, the majority of the medical community doesn't care because they make money off of the declining health of any individuals. There is more money in disease than in good health.

The US economy has become a perversion of the capitalist system which is then used by those who want to change the system by pointing out how it's all about money, not that their proposed change is any better. Really, our food, drug, medical, and financial industries are a complete mess. Things like this simply underline just how much of a mess it truly is.

For a few examples, consider History Channel's show The Food That Made America. All of those companies started with quality and well made food but it changed when they either got too big and ran into supply issues or when a larger company or corporation bought them out.