It was still common up through the 1920's for people who had lived in the South for generations to have a still-living relative who had fought in the Civil War, and that relative was always a Confederate soldier; there was never a Union connection. That's why there's still a Confederate preference: great-grandpa was a Confederate, never Union, and if you celebrated your heritage it was always Confederate since there was no Union background.

Celebrating Union things in South Carolina makes as much sense as celebrating Confederate things in Chicago.