The Midwest may have a low density of cars, but the arable land is largely farmed; it isn't pristine, untouched wilderness.

I was born on a farm in rural Ohio, so I can appreciate the difference. I'm thinking more of Wyoming.

But that land is probably not suitable for farming - because if it was, someone would probably have a farm on it. So then you're comparing soil-not-great-for-farming from then and now, which is something, but it's not what we really care about (soil-used-for-farming).