Plain and simple....
1) Supply and demand does not always provide "cheap food" if it works as it should.
2) Government steps in to keep food prices down so they still have peasants to stay in production to produce a product "below parity prices"....therefore cheaper for the consumer (voting public)
3) Abundant food/cheap food makes people happy. People go hungry or outrageous food prices and people will be no different than hogs when feeders run dry.....could end up with a bunch of "tail biters".