re: What is your hypothesis for the conservative decline in the suburbs.

As the economy improves as the result of conservative policies, the economic situation of individuals also improves. As people become financially stable, they become more supportive of social welfare programs and more progressive ideas in general.

It is simply a case of people taking their eyes off the ball due to their own financial/economic security, and they forget what policies led to their economic security in general. It is a cycle.