I'll put my money on one of two reasons, possibly in concert with each other:
1. Youthful pilot
2. Alcohol
A third, quite common ocurrence would be the opposite of #1. Our town just scrambled about $500k worth of equipment and a good handful of men to pry a couple in their 80's out of their Caddy after they rear ended another driver on a clear, flat, straight, dry road last week. They were not wearing seatbelts. My understanding is that it was not pretty.
I have to wonder if there was some sort of topographical influence, or merely a distribution of weight involved in the counterclockwise rotation of the projectile.