Subsidies are the symptom. The reason is fed govt ability to create unlimited spending. The reason for that is 3rd central bank known as 'Federal Reserve' which manipulates interest rate on govt debt issuance.
Subsidies in general are enabled by deficit money printing which would presently be unaffordable without interest rate suppression.
Farm subsidies take various forms such as tax preferences, import tariffs, and a USDA organization specifically tasked with manipulating crop prices.
https://www.usda.gov/ccc
