I never quite understood how the majority of agriculture cultivated in the US is grown in an area not suitable for agriculture (Sun alone isn't enough. Having n

I never quite understood how the majority of agriculture cultivated in the US is grown in an area not suitable for agriculture (Sun alone isn't enough. Having no water obviously is a problem, as can be seen in droughts like these). America is such a huge country with a huge variety of climates, microclimates and arable land. Why you need to put everything in (basically) a desert is beyond me.