I'd say wages/unions no doubt are a factor - part of the overall lower "cost of doing business" that includes everything from taxes to real estate costs (which are themselves reflected in wages...)

"Right to work" (anti-union) states are definitely an attraction. The article also mentions incentives and willingness of local governments to work with companies to help with relocation. Incentives are made possible by shifting taxpayer money from things like education and health care to corporate incentives.

I think the underlying reason for all of this is that the South is playing "catch up" in transitioning from an agricultural economy to an industrial economy, which has already passed us by, and on to an "information and service" economy, whatever that is. I guess that means we'll all be doing each other's laundry and e-mailing someone overseas when we need a patch downloaded to our washing machine. Or something.