This image tells part of the story:
It sure looks like government subsidies control why it is so cheap to get hamburgers, and conversely so expensive to get good fruits and vegetables. Funny that the subsidies are such a poor match to the government’s own nutrition recommendation! Could there be some political motivation for the lack of subsidizing what the government claims that we should be eating? You can read a New York Times editorial on this here.
Side note, the attempt to add a third dimension to the graph and the pyramid shape makes me cringe, since I’m pretty sure the sizes of the relative groups are deceiving. For example, on the right, the orange represents 6 servings while the tan is 11 servings. To me, the tan looks much more than twice as big, even though 11 is less than twice as big as 6.