Because those metros aren't large. If you look at the metros with Dem trending suburbs, DFW, Houston, ATL, Phoenix are all top 10 on the list. Nashville is relatively small and not even as big as Indianapolis. The smaller the metro area, the more Republican the suburbs are.
Even within the city limits of Memphis and Nashville, there are suburban communities. I guess middle class minorities are still finding homes within the city. While a crowded place like Atlanta requires them to leave the county
Memphis dips into Mississippi, and to a lesser extent, Arkansas.
