I think the answer that makes the most sense is the idea that Michael Morris mentions, relating to sentiment and nostalgia--

The "South" mentioned in songs is a sentimental place, kind of a place in the heart, not a real place, which represents home to everyone who feels displaced--

"Back East" tends to be used for home in songs in the same way, but "Out West" tend to represent aspirations and dreams, both realized and unrealized--"Up North" is used like "Out West"--