I genuinely don't think it's a stupidity thing. It's a core values thing. Core values we don't have in the UK (we are largely atheist and slightly socialist as a nation).
This means we just don't get It because we dont share values.
Fear of change is definitely a factor having said that. You have to see that through the idea that the coasts have lost touch with god and the crime rates have risen etc etc. If you live in a flyover state you are much less likely to have ever left the country so why would you feel responsibly to be involved in global politics? You would prioritise your taxes being spent on fellow Americans because of your narrow world view.
Again we have this mentality to an extent in the UK. It manifests slightly differently and we have much higher levels of willingness to be involved with the rest of the world due to our history and more mixed society (yes even in very white areas - we travel abroad more).
Its fascinating to see DNA profiles of Americans from the coasts versus the mid west, the likes of Alabama, utah and then the south near the mexican border. It highlights migration and isolation patterns. I had no idea about how salt lake city is very English and Scandinavian in Ancestry. Or how Scottish and Irish other parts of the US and Canada are. Or how mixed the coasts are by comparison.
It is going to have an impact on attitudes. Not necessarily in terms of race, but in terms of values.
If you come from a family that emigrated for religious reasons from Europe and then became utterly devout, then you are much more likely to retain those values if the community your ancestors lived in was like minded and had little outside influence. Even for 200 years. I think I get back to the 1840s in about five or six generations. The sheer size of America is highly relevant here.
I don't think it's necessarily a hostility to change as such but is about the rate of change. Some places have changed much faster than others and haven't really considered how them dictating the pace is a problem. It's about being told what to do and how to think. Something that doesn't go down well on either side of this cultural divide.
There's the meme of the left running away whilst the centre has stayed still and is now perhaps closer to the right that's very apt here.