The incentive for me is I can do other things. When I drive, I focus on driving and the radio/podcast/audio book. If someone, or something, else drives, I could read a real book, nap, do email, play games, whatever.
As others have mentioned, it also greatly reduces a huge point of failure in the whole driving thing . . . driver fatigue, human error, etc. No more opening the window in freezing temperatures and sipping on the 5th cup of gas station coffee to make it to your parents for the holiday . . .