Even if you can manage to stay alert for so long, wide parts of the population cannot, which is why maximum limits have been introduced for commercial drivers everywhere (and accidents rates have fallen correspondingly), and why in accidents drivers who have been on the road too long are generally found to be at least partially at fault.

Additionally, who says you're actually able to drive safely after 13 hours and react to something like, let's say, a child hopping in front of your car and that you just have been extremely lucky?