I've been around motorsports most of my life and I used to see this all the time at racetracks in America. Even in NASCAR country, lots of people assume the "good ol' boy" accent means a person is just a shade-tree mechanic even if they're the most well-educated person in the garage.
For most of the rodeo he spoke with a thick drawl, obviously going for the "good ol' boy" vibe.
A few times, he slipped up and spoke with a very plain Portland/PNW accent. It was jarring when I heard it but he went right back to the good ol' boy accent and I don't know how much anyone else noticed. But it came across like it was all an affectation, for the reasons you described.
(He also occasionally herded his cattle by sticking his head through the roof of an ancient VW Beetle. But that's another story.)
I've lived in Appalachia my entire life (West Virginia, Georgia, Pennsylvania, and New York).
Although I can't generalize about the people of either the Midwest or Appalachia, there are some big differences between rural Appalachia and some other rural places.
1) Landscape. Due to the difficulty of building roads, some Appalachian places (closer to WV and KY) were extremely isolated until the 20th century. This affected culture, education, wealth, and industry. It's a huge factor in the region even today.
2) Agriculture. In most of Appalachia, you can't have a massive corn plantation. You rarely see a large field of anything at all. Most of the exports are capital-intensive and extractive (mining or timber), and the result is that there's a pattern of wealthy outsiders plundering the resources and leaving locals with little of the gain.
3) Stereotypes. A strong Midwestern accent (from, let's say, rural MI or PA) does not have the same connotation as a strong Appalachian accent (from KY or WV). The stereotypes of the regions just aren't the same, and they do affect people applying for jobs.