Having been on the 550 many times, my thought is that it just isn't for a lot of people.
I have seen motorcycles going 15 mph just barely able to stay up right because of the fear. Motorhomes, well lets just say they don't like the edge and stay away from it forcing people in the oncoming lane to outside of their lane.
Then there are the near death experiences from stupidity, I have see more than one car forced off of the road because of, well stupidity, better than a head on to go into the ditch. Big rigs are a problem, horsepower is not the issue, its just that they cannot maintain the speed, although low in a curve and coming out of a curve they cannot accelerate like a car can. cars will stack up and then someone tries to make a pass.
Go early in the morning to enjoy it.