If you can, you’re rotating beans and corn every year. (“Roundup ready” of course)
Wheat is on the marginal drier land. Not that they couldn’t plant wheat there but beans are way more profitable and so they don’t.
The plains is by definition more arid, marginal land a step up from pasture/grazing.
A lot of traditional wheat/sunflower/barley/oats has gone over to beans and corn bc roundup and GMO.
On my family’s farm I don’t remember the last time we had wheat crop but that was our staple for like 50 years.