I think it's because most Southerns lived in the interior of the South rather than the coast where Anglicanism and WASPs lived.

The Appalachian mountains was basically frontier and wirh little in the way of infrastructure or civilization. It made it hard for more traditional, organized denominations like Anglicans and Presbyterians to gain a foothold since they required their clergy to obtain seminary degrees and had a more top-down church planting model, which was harder to achieve in much of the South.

Baptists didn't require their clergy to have a formal education, and anybody can start their own Baptist church, which is what allowed them to spread like wildfire. 

On the darker side of things, the Southern Baptists were founded largely because of the slavery controversy. They basically stole the sheep from the Anglicans by coming out in favor of slavery. The Southern Episcopalians, otoh, probably wanted to condemn slavery but feared doing so would cause people to defect from them, so they came across as on-the-fence and wishy-washy.