It's all about proper irrigation. Some farmers are just plain ignorant as to how to do it, or don't want to put the work in that's required (and yes, I come from a farming family, there are lazy farmers).
Then you have to consider the cost and preparation involved to do it. Setting your land up for proper irrigation is not a light task. It involves sitting a season out, and spending an entire year preparing the land. You have acres upon acres of land that would require surveying and properly grading the land for irrigation, digging irrigation ditches without getting killed (which is a big cause of accidental death on a farm due to collapse), and running these all without screwing up the tramlines and cutting yourself off from your crops. It isn't an easy task, and it isn't a cheap one.
Since most farmers barely live year to year as it is, they are generally not in a position to take out more loans than they can pay back, on top of sitting out a season, and working essentially from a 2 year deficit when they get back up and operational again.
With the area involved, it isn't as simple as taking out a hose or putting in a sprinkler system. Even then, you need groundwater to supply those systems, and without a good irrigation plan in place, and a low water table, it's a lose-lose situation.
Proper irrigation. Plain and simple. Ditches and ponds everywhere. But even then, a good enough drought takes that all away. You can't win every battle. Or afford to fight it.