It's not just about short term vs long term gains for the farmers: it's about gain for them vs gain for the whole human population (the second involves just a small marginal gain for the farmers).
You'd be surprised about the shortsighted things people do for small marginal gain.
More of a light hearted example. I worked at a grocery store years ago, one summer the 4L ice cream buckets stopped having handles. A lot of people complained, they liked to use them for berry picking and other things. One day I asked the people we ordered the dairy stuff from why. Turns out, some accountant figured out they'd have a marginal gain of 1¢ per ice cream bucket if they removed the handles. In the end though, that year we ended up throwing a lot of them away, whereas the summer before we'd had trouble keeping them in stock. People really liked those bucket handles. I still wonder if the penny savings were worth the loss in sales from people that wanted buckets with handles more than ice cream.
