Not op, but on the business/sales side ‘midwesterners’ tend to put people at ease and are decent communicators. In my experience they’re also the clearest American speakers, so non-native english speakers have an easy time understanding them. Coming from an area (at face value) that is not widely desirable or well-known gives a decent perspective on the ability to perceive value for others and speak plainly to sell it.

Part of the above in my opinion is due to there being a far smaller gap between the wealthy people in the area and the poorest both financially and physically. A plumber, doctor and retail worker can live on the same street as homeowners. Not to knock the coastal cities too much, but contrast this culture to homeless people sleeping right outside a $3200/month flat, or primary teachers living out of their van, and you can see how it can have a different effect on those who are raised in those areas.

My cousin has a theory that the (sometimes brutally cold) winters and generally blue-collar background breed a bit of "suck-it-the-fuck-up-and-get-it-done" mentality.

I think that depends a lot on what your basis for comparison is. It's sort of like asking what California or New York culture is: what people notice is the differences to what they're used to.

One of my coworkers who moved to Michigan after being all around the U.S. described the culture as people who were genuinely nice and caring. YMMV