The most likely reason that someone today might decide to move from a city in the Midwest to the South is A the decline of manufacturing in the Midwest.
While options B (high-tech jobs in the South) and C (urban overcrowding) could also be contributing factors for some people, the decline in manufacturing is a significant economic driver that might prompt individuals to seek better job opportunities in regions with more growth in different sectors, like technology in the South. Option D (higher housing costs in the South) would generally discourage migration unless counterbalanced by other advantages, such as better job opportunities.