The problem is really quite simple: Americans overeat Processed foods are part of the problem (in that they are tastier and easier to consume than "rawer" foods), but increased wealth and ability to consume food is also a part of the problem Food has literally never been cheaper and tastier
Even quick snacks found at U.S. gas stations (when I'm running late) consist chiefly of mass-produced, sugary, heavily processed desserts like Twinkies and HoHos, whereas options for fresh fruit and locally made goods with natural ingredients are often not to be found. I take a pass and look for an open supermarket instead. I doubt that it is a supply chain issue: in the north of Scandinavia and Canada, the outback of Australia, and especially through Asia it is almost always possible to get somewheat healthy quick snacks of a local variety at roadside petrol stations.