if you have read the book "The Big Sort" then you will have the answer to the OP's question.
That's pretty much it. People have exercised their right to live whereever they want and its generally with people just like them. Crazy rednekcs want to live where there are other crazy rednecks.
But why don't they move to a more inner suburb?
People who live in the city are used to having crossing guards at every street corner, so they accept nannystatism. They reason that were it not for the state, they would be limited to their own block and couldn't work or get food. They have effectively become both physically and mentally crippled.
Those who live in the exurbs, realize that after they drive down to the mailbox to pick up their mail, that they can keep on going and drive to the Walmart or their job at the munitions factory. They become empowered and self-reliant.
Presumably they built those roads themselves.
After they cleared the forests, tamed the rivers, and broke the sod.
Exurbs, especially ones in the south plains, probably have the highest rates of both people who both make $50,000.00 a year (80th percentile for individuals, 45th for households) and have been convicted of a felony. Most of which convictions arise from when a gun is pulled over kids crossing their fence or some guy staring at their trophy wife.