It’s because of the Mason-Dixon Line.
So why don’t we call the North Masonie?
Because it sounds like “Masons”, and everyone knows they were/are an evil secret society intent on world domination.
Union troops used to sing “Dixie” on the march, which goes to show you something.
Northerners used to be called “Masonites”, but ran afoul of trademark laws.
if you look for Dixie State Univ. in the South you won’t find it there.
Northerners are called ‘Yankees’ in these here parts.
Now figure that one out.
My dog is called Dixie because the other one is called Doxie.
Make sense?
That makes perfect sense.
I knew you would understand. And it completely explains Trixie.
#3.
To expand on this, according to a sketch published in B.A. Botkin’s 1939 Treasury of Southern Folklore, the reputation of the Banque des Citoyennes de la Nouvelle Orleans was so strong that its “dixie” notes were accepted up and down the Mississippi valley; but the word was associated with Louisiana, the “dixie’s land”.
Some time in the early 1850s - there’s no certain date - the Ohio musician Daniel Emmit wrote “Dixie’s Land”, which spread the nickname to the whole South.
In other words, “Dixie” has nothing to do with the Mason-Dixon Line.
But you will find it in Southern Utah, which was settled by Mormons from the South.
People in Southern Utah speak with a different accent than people from the rest of the state.
That never occurred to me. 
So I guess my state is frontin’ by calling itself the ‘Heart of Dixie’.
Dolly Parton has a music place that used to be called Dixie Stampede but she changed the name to Dolly Parton’s Stampede partly because she did not want to offend people.
When I was in college, my school was a member of the Dixie Intercollegiate Athletic Conference. In 2003, after my alma mater had left, the league rebadged itself as the USA South Athletic Conference.