They're adapting to the south. These are not the Bill Clinton years anymore. They have been moving rightward for some time and unfortunately for Dems don't look like they will go back. Although I don't know why in particular the've moved rightward, white voters in these states didn't always used to be as right wing as the deep south, now they're almost as right wing as the deep south with >80% in Louisiana, >70% in Arkansas, and >70% in southern Missouri (>60% overall).
There must have been some backlash with white voters and I'm guessing a lot of that has to do with the party moving farther to the left. Just like there is backlash with Virginians with the republican party moving further to the right, etc. This looks like it will stay this way and some democrats have got to accept it as they have dominance over the republicans at the moment (You guys should be happy). Thinking AR, LA, and MO are going to move leftward again is the same as thinking OK, and eastern rural Texas will move leftward. Whites in OK, and eastern rural TX took similar trends as whites in AR, LA, and MO.
Bottom line: These trends are part of the democrats problems with white voters, here's a great article to read
here. Just like republicans have a massive problem with non-white voters, democrats have a problem with white voters, but their problems are under emphasized because they're currently winning.
Here's another article
here on a republican strategy to "double down" on white voters.
