The speculation is that Google Maps or Mapquest or something else, without regard to local conditions, generated a map which would do that.
As I understand it, that's part of how they eventually located the car.
I wondered if it was something like that. Having been raised in mountainous country, I know that the most direct route can often be the most dangerous if weather is capricious. I wonder about the safety of naive urban folks who slavishly follow their on-board GPS systems in unfamiliar mountain or desert terrain. Weather, both cold and hot, can be mighty unforgiving to stranded travelers.