In 1984 in particular you also have the use of minority (mostly AA) voters by Democrats in the South.
They controlled pretty much all redistricting and carefully dispersed AA voters in as many districts as possible to give themselves a base.
This meant a Democrat needed only 35-40% of the white vote in most districts and was thus protected.
When civil rights groups sued and forced majority minority districts in the 90's this helped contribute to the GOP transition.