Living in a conservative country area I notice racists escaping here, and they seek sympathy with local people. They join churches and bring a lot of money, so the locals tend to rally around them with the intention of encouraging them. Older people also hang around yelling at everything wrong in the world, and younger people have to move to follow opportunities. The young families that come back tend to lean pretty far right.

Then there's farmers and primary producers that need left leaning people to be ostracized, so that they can exploit whatever resources without environmental oversight. They also tend to encourage the far right atmosphere in local towns.

The remaining leftists are a minority that tend to cling to one specific town and the most populated city here. But, they even seem compromised when compared to big city leftists. Some appreciate racism, etc.

All the other answers here cite things like education and wealth, but spend time in politically-tidally-locked places like Rochester and Syracuse and you’ll realize all it boils down to is it being cultural. There are what many would call right-leaning cities, and they aren’t any different race-wise, ethnicity-wise, education-wise, or (most of the time) wealth-wise except that they’re right-leaning. Education/exposure does not magically change your whole philosophy, that’s like saying going to a Catholic school will guarantee your kid will be Catholic.