The most notable example here (hardest to explain) is Louisiana.
Louisiana really fits into the same reasoning you posit for states like MO and OK - the states are pretty much already maxed-out for Republicans without any sizable “Romney-Clinton” type suburbs.
Of course, that characterization describes a good deal of Southern states - MS, AL or TN, for example - that did see county shifts from 2012 to 2016. In these states the flips were exclusively Obama/Trump flips in rural, slim plurality/majority Black counties. The handful of Louisiana parishes that fit this profile (really just St James and Iberville) stayed marginal Democratic wins.
