One factor is narcissism.
It's hard to be a narcissist in a rural area. Sure, there are some, but it's difficult to maintain. The backbone of the economy in rural areas tends to be the land, in one way or another. It may be farming, forestry, mining, or tourism, but the land is generally the commodity that sustains people.
If one has a belief in one's own superiority, it's difficult to work on the land. The land is humbling. A farmer can't say "with my genius, I can insure that this land will have the greatest yield it's ever had!" In general, a farmer has to use time-tested techniques to the best of his ability and hope for the best.
Someone running a resort by a natural wonder can't wake up and say "I'd like to do a deconstructionist theme this week" and hope to attract tourists. The resort owner knows that people are coming primaily to see the natural wonder, and all he can do is cater to their needs as best as possible.
Urban environments have room for narcissism. Perhaps someone wakes up with a belief that their personal vision in art or religion or policy is the best for the world. Because of the increased contact with people, the narcissist can sustain himself by convincing a small percentage of people he meets to buy into his vision.
Now, what does this have to do with politics? Conservativism is repugnant to narcissists. The conservative philosophy does not require an elite group. The emphasis is on the limitations to what humans can do. Experts can't decide prices as well as the marketplace, for example.
Likewise, liberalism attracts narcissism. Liberals believe people can change the world and that "experts" can do things that people can't do on their own.
Thus, narcissistic people tend to seek the cities and those with some humility will tend to seek the country. Millions of people living in the cities once lived in the country, and vice versa.
Very good answer.
Urban areas also seem to provide ample audience to support the narcissist. Since they don't really produce much of value on their own, they need more external economic support from those who will pay for the narcissist's "superiority". i.e. A farmer / miner / lumberjack will likely not be willing to spend hard-earned money on a piece of art, where a city-dweller would be much more likely to.