I don't think it is more prevalent in those areas. It is quite diverse, scattered across the US. When I was involved in it ages ago, when numbers were quite small, there were still groups in every state.
Here's a link to some homeschooling groups in New York.
Our group also included several school teachers and a few college profs. We had dentists and medical doctors as well. I think the diversity of professions was interesting, I don't exactly live in a booming metropolis.
So, it's not limited to the rural south and midwest.
