Song of the South, the movie, takes place in Georgia.
Splash Mountain, the WDW ride, does not. That's why they changed the landscape, the music, etc. Bears, foxes and rabbits live West of the Mississippi too. Even riverboats operated out west. They translated the story to a western setting because without any references to plantation life, it doesn't have to be set in the South East.
The proposed Tiana ride is about preparing for Mardi Gras. They're not even trying this time because the California designers wen't thinking much about WDW when they made the decision, only what would fit in "their" park.