If I could only name two big "things" that contributed most to the obesity problem of today it would be:
- Agricultural Act of 1970 and the polices of the 1970s, resulted in corn so cheap and abundant that other industries actively looked for usages. HFCS was obviously one such use, and it out-competed all other nutritional sources on price.
- The 1990s "fat bad, sugar good" which resulted in reformulating a lot of staple foods and the beginning of standard sweet food allowing the cheap HFCS to flow.
The US needs, and has needed, to offset the corn subsidies that get turned into HFCS by adding a "sugar tax" at the consumer side. That way it can still exist for animal feed, and be used where appropriate without being unnaturally and unreasonably inexpensive.
The reason they don't is that it is political suicide to suggest sugar taxes in personal-freedom loving US that is pretty anti-tax regardless.