The “shockwave” occurs because people tailgate. When ANYTHING happens, or even looks like it MIGHT happen, they are forced to break because they MIGHT run into the car they’re tailgating. By maintaining a “proper” distance between cars, you aren’t forced to break the very second something looks like it might happen, and therefore break up the formation of the wave.

That only works if traffic isn’t so heavy that cars are forced to tailgate. But it’s why shockwaves form even in light traffic – most people tailgate regardless of whether they need to or not. The best way to improve traffic in the future is to make cars that keep their distance regardless of the driver.