There also tend to not be as many people driving around slowly gawking on the roads themselves (unlike Zion or Yosemite, say), since most of the park doesn't have crazy vista views, it's mainly a high altitude, flat-ish volcanic plateau in the middle. The specific sites along the roads will have the traffic mostly.
Also, as a photographer, the shuttle system is pretty awful. It's no longer easily possible to do get out to where you want to be well before dawn.
Then went to Grand Canyon and Zion and saw they have shuttles which are sometimes exclusive (if the shuttle is operating you cannot take the road), which makes so much more sense, and even allows for more flexibility (you can go on a hike which is out, and not have to walk back the same way but hop on the shuttle bus).