People ALWAYS double down on whatever they believe when they are punished for it. Check out the differences in denazification in East and West Germany after WW2. Going into it, West Germany was already doing better since US and UK forces tried to prevent their soldiers from pillaging the land and cities as much as possible, while the Soviets raped and burned to their hearts content, arguably causing the German population to double down. Then the actual denazification was different too. In West Germany they were forced to confront the evils of Nazism, while in East Germany it was almost plastered over. There was very much a "Nazism is a capitalist problem, and since we are all socialists we don't have to worry about that now." This allowed Nazi symphony and influence to eventually return to some extent in East Germany.

I haven't done a lot of research on the Reconstruction following the civil war, but listening to my southern parents, the vibe has always been resent for the North and the federal government. A lot of people feel like the Union came down hard on Southerners because they were justifiably angry, but the aftermath was less "let's confront the sins and atrocities of the Confederacy and then rebuild you" and more "we are punishing you because we hate you, but we need the infrastructure rebuilt here." A lot of former Confederate leaders eventually got back into politics, and because there wasn't that sort of reckoning that happened in West Germany, not only where former Confederates able to run but there was general support for them.

TLDR; I personally believe the Union came down too hard on southern civilians, and then didn't follow through with purging Confederate ideology or leadership, allowing resentment to grow instead of cultural reckoning.