Personal opinion: Because some food should not be that cheap. It’s part of the reason we are so fat in the US (plus car centric cities). Subsidies keep some things like corn artificially low and they end up being hammered in into every product (biodiesel, sweeteners, animal feed, etc.). With that setup, companies have learned to use those subsidies and other workarounds and loopholes to maximize profit at the expense of the product being output and we fall for it every time .