I'm not a big supporter of farm subsidies either but I understand the driving force. Two words ...
FOOD SECURITY
If you look historically at how Ag Subsidies started around the world it was usually a result of weather (i.e. The Dust Bowl in the 1930s here in the U.S.), economic downturns, wars (especially WWII) that lead to food insecurity issues within these countries. The war in Ukraine is a classic example of this today as they have some of the most fertile farmland in Europe taken out of production and also had trouble getting their grains to export markets thanks to Vladimar. Europe and Japan had major food insecurity issues in WWII and as a result put huge subsidy plans in place after the war to make sure that did not happen again. One of the major fears among Chinese leaders is feeding their people ... hence, huge subsidies and state run farms.
Yes, U.S. subsidies can seem high but they are actually relatively low if you compare them to Europe and much of Asia. I wrote a white paper on this probably 15 years ago for my employer but here is a better one by Alice Calder that has the most current data.
An explainer of agricultural subsidies around the world, why they were implemented and what issues have risen.
www.hinrichfoundation.com