Some African Americans, they wrote, “might wonder how Mayberry came to exist as an all-white community and what this signaled about race relations in the quiet hamlet,” also noting that Griffith said he regretted the decision to exclude blacks from the regular cast. The actor explained that African Americans at the time did not want to be portrayed in servant roles and “there is no way in some small town in the South that white people were going to flock to a black doctor or lawyer.
It makes sense. Well, a truly southern town would have a lot of blacks – minus ones in Appalachia. Nonetheless, Mayberry is in Appalachia also I think (The Blue Ridge Mountains).