Another possibility is that people were just sick of him after so many years. Even Churchill lost a reelection bid soon after winning WWII. People sometimes want to make a change.
Nope. The Louisiana RINO contingent didn’t want a real conservative as governor. That’s why Darden and Angelle, both card-carrying RINOS, ran against him, and cut him up.
You've got something there. Vitter was not part of the GOPe, as we define it, but he was definitely an old face in Louisiana politics. In a way, this race is a confirmation of the "year of the outsider" narrative.
Also, speaking objectively, Edwards' advertising campaign on "prostitutes over patriots" was devastating. The Democrat base may not care about such issues, but the Republican base does. It's a political reality, and railing against the base does no good at all. The R's may have been asked to hold their noses one too many times, especially when confronted with an attractive alternative.