Many are here because of the lack of income tax, the country music industry, and the extremely culturally conservative government. They either do not care about the poor public transit/services/infrastructure/schools/etc or they do not care enough to outweigh the benefits.
A common refrain I hear when talking to people is that they wanted to move somewhere that wasn't so "woke."
Nashville also, until recently, had a low COL compared to similarly sized non-Southern metros.
Personally I am here for work, and realistically many others would do the same. Nashville has more employment opportunities than the deep south and is a logical place for such people to end up.