Corn is left over subsidies when they were thinking they would make bio diesel in the 70’s. Mostly it was back scratches to get legislation passed quid pro quo in congress. You vote for my bill and I will vote for subsidies for a crop that grows well in your district. The idea was to secure that farmers will grow crops and maintain food security but with the current dysfunction in congress, and the emergence of corporate farms killing smaller family farms it is really just a joke now.