Grains raised for animal feed or producing ethanol are commonly unfit for human consumption. Every crop is highly optimized for its intended end use. You can't take existing corn stocks beyond what is currently used in food and convert it into food, the varieties planted are not meant to be eaten by people. The supply chain that supports these crops is also optimized with assumptions about the end purpose.

It would be possible to re-plant that land with edible crops but it is not fast or simple.