Nothing "drives" people to that sort of humor. The people who get offended by jokes that are based on stereotypes are just so close minded. If they understood that jokes dealing with race or something "offensive" were just based off stereotypes they wouldn't get offended. Jokes are jokes, they aren't meant to be taken seriously or ever regarded to having any significant truth. I do 'offensive' jokes sometimes, because cheesy jokes like why did the chicken cross the road or sesquipedalian humor isn't often understood. Stereotypical humor is often understood the most and has the most humor. When someone gets offended, its a personal problem, not the other way around.