These parts of the country have been booming for 10(20?)+ years.
Yes, the parts of the country he visited (especially the Black Hills) are full of the same crappy towns that have always been there. The Black Hills region, although naturally beautiful, is covered by a blight of ramshackle old buildings and trailer homes. And so it has been for some time.
However, It is IMHO no worse than the outskirts of Philadelphia which I visited for the first time as a high schooler. I won an essay contest and was sent to Valley Forge. I couldn't believe what a sh*thole Philadelphia was and the surrounding area. People sleeping on the streets inside the city. People sitting on rocking chairs on the porch of old ramshackle cabins outside the city.
Again, what do you make of that? People are the same all over. I'm really tired of this "people who live in X are Y" crap. Whether it's America vs China vs Europe or Red State vs Blue State. It's mostly bunk generated by our own biases.
Sure, there are people on "tough times" but I can't believe that it's the "nastiest part of the state."
Of course, these are just my personal observations. I lived on the "good side" of town and my father (who owns a construction company) did fairly well.