As raw materials suppliers, farmers will always have relatively low incomes, compared to the rest of the food and agriculture economy. Farmer's have been taught that yield equals success in farming. Unfortunately not many of today's farmers have had the benefit of that counsel. We acknowledge the highest yield producing farmers, not the highest value retaining farmers. The Corn Producers Association regularly recognizes the farmer with the highest corn yield.
Seed companies compete on the basis of the highest yielding varieties, etc. etc.
A little late, but better than never. Farmers have been taught to define efficiency purely in terms of labor efficiency. No one would argue that the industrial farms of the global economy are among the most labor efficient in the world. The problem is that labor efficiency is only one of three critical efficiency measures. Energy and capital efficiencies are at least as important to economic survival.