First of all, though many are horrified by this suggestion, Dems and Repub principles essentially flip-flopped c1915. Sorry, but Repubs were the statists.
Then, stubborn Southerners, unable to let go of the Civil War especially if they or their parents had any history with it, refused to recognize this fact long after. Grandchildren and so on finally starting seeing this generations later. Hence the growth toward Repubs.
May you also note how Northeast was the Repub, and has long been known as commie Dems.
There is a reason for this. They are not the same parties.
They supported a stronger federal government back when no federal government would be as powerful as it is today.
But Democrats found their own ways to be "statist" back then, whether we're talking about Jim Crow or W.J. Bryan's plan to nationalize the railroads.
The Democrats, who used to call themselves "The Party of Personal Liberty", went over to the dark side in 1896 when they nominated the Progressive William Jennings Bryan.