People will tolerate an oil shortage more than a food shortage. Plus farmers can always blame the weather, and there is the perception that they are all hard workers. If everyone was to trace back their family tree, there will be a farmer in there somewhere. Most people have done some gardening and they know things don't always go well. Whereas oil producers are all perceived as JR Ewing.
My Grandfather was a farmer, along with my Uncle and various relatives to this day. My Grandfather became a stanch Republican because of FDR and his farm program. My Grandfather's farm is still in the Family and now his great grandson is farming. Know all about farm subsidies! :)