There are also cultural differences in these low cost USA areas that will make it hard to find educated techies there and/or get them to move there. Like it or not, the socially-liberal urban-California culture has become a sort of "Defacto Standard Culture" for tech, and a company is not going to be able to simply move all these people to rural Alabama because the cost of housing and living is cheaper there.
When work-from-home became more widespread, my spouse and I did the whole "Oooh, where could we live to maximize our income/expense ratio!" Zillow fantasy-exploration, and we concluded that even though many places in the country are significantly cheaper than where we are, we would be miserable in these places.
Reminds me of that story that made the rounds on HN a few years ago about that techie who moved to Bumblefuck Arkansas and bought an insanely cheap office for his tech enterprise, and regretted it for years due to the place otherwise being a total shithole.