Because their parents were racist and raised them that way and the reason their parents were racist/prejudiced is because their parents were and the cycle continues. Slavery in the U.S. started and grew very big there in the 1800's. A lot of people hold preconceived notions and are set in their ways in the South and they are hard to shake of them for whatever reason. There's a lot of "old money" in the South that dates back to plantation days as well. It's got a sad, complex history.