I think if anything, it's just that we're more....comfortable (for lack of a better word) with racism here. It's worth noting that the South also has the largest (by percentage) African-American populations. Which, IMHO, creates two different kinds of racism.
In the South, it's a "familiarity breeds contempt" sort of thing. Racism tends to be generated out of all the little petty squabbles and inter-community competition for resources, and race is an easy target. Point of example: my late grandfather, while a saint of a man, was also a product of his upbringing. If a white guy cut him off in traffic, that was a "dum-dum". If a black guy cut him off, that was a "dirty n****r". He wasn't particularly any more incensed than he was with the white guy, it was just easier (and ingrained) to denigrate their skin color than their actions. But at the same time, I feel like it's a mile wide and only a few inches deep. Put five black college kids in Carolina blue basketball uniforms and put them on the court, and those rednecks will be cheering them on like they were their own children. There's almost no job here (other than maybe corporate executive) where you're not going to have at least one black co-worker. And chances are, they're going to be a pretty decent person. Which is why you get a lot of cognitive dissonance like "Some of my best friends are black" and "There's black people and then there's n*****s".
Meanwhile, you have places like Idaho, New Hampshire, Montana and Arizona that are hotbeds of violent, strident white supremacy and have almost no African-American population. In the absence of living, breathing black people to remind you on a daily basis that they're just like everyone else, it allows those supremacists to demonize and dehumanize and caricature minorities to the point that they can self-justify radical violence. The racism there (where it exists) is narrow but deep.
And it's often multi-faceted. My mother was born in Montana, and her mother's family was racist on a different tack: black people were more a curiosity than anything in Montana. But Mexicans and Native Americans were strictly verboten as potential mates (because after all, they were the hired help). Which of course, meant that two of my grandmother's sisters promptly married a pair of Mexican brothers who were farm laborers. Funny how that works. And then my family themselves were Volga Germans, which meant they weren't fully trusted by the US during WWII.