The market isn't free; there are government farm subsidies in all the wrong places. It's no coincidence that cheap junk food is built on a subsidized corn industry.
Humans are still hardwired for the state of nature where high caloric foods are a scarcity, evolution has not caught up yet. It is very silly and unrealistic to suggest that raising the profit motive above others will bring out the best results in every sphere of human endeavours.
