I guess because it's red, but has some blue elements and white stars...and we all know, red, white, and blue flags with white stars are irredemably racist... /s
I was looking for a Tennessee flag to fly along with my US flag the other day and I noticed that one of the big-box, home improvement stores offers every state flag except for one, Mississippi. It appears to be a policy that predates the latest battle flag uproar. Ironically, a person of that state could buy the flag for mexico from them, just not their own state flag. They have no qualms about doing business in Mississippi though since they have over 100 stores scattered about.