Not only farmers. Consumers as well. Farmers can only grow those crops for which there exists a buyer. In many areas, even in farm dense Europe, you can physically only sell like 3-6 crops in bulk. Now a farmer can sell directly to consumers but then that farmer runs a shop business next to his farming business and that's not realistic for everyone. Especially if you grow over a thousand tonnes of a certain grain.
It may well be that, for example, sorghum or millet is a much better climate adapted crop to a certain region than bread wheat. But that won't matter at all if there is no local buyer of those crops. In my own country for example we have successfully shown that quinoa is excellent to grow here because the Andes mountains and Sweden surprisingly have similar climates. But if you go into a shop you can still only buy Peruvian quinoa. No local buyer exists and local consumer demand is too low for an infrastructure to be built up around it.
So I say don't put all the pressure on the farmers themselves. They are working in a system that forces them to grow certain things a certain way.