I've seen it personally and it's become a regular feature of life in Washington--one of those little things that give a city its charm. The problem with your suggestion is that they don't have the math processor to calculate whether a car half a block away is going to stop--or is even capable of stopping. Vehicles are not as nimble as predatory animals, but they move, accelerate and decelerate much faster. The deer don't have the necessary intuition to base calculations on that. Even if there are no human pedestrians around, they understand that cars are far more likely to stop at a crosswalk than anywhere else, and even more likely to do that if the little green light is on. Perhaps more to the point, waiting for cars to stop, even when the pedestrian light is on, can be a vain hope. If there's no foot traffic in the crosswalk cars from the cross street--who also have a green light--will make right and left turns across it. Even human pedestrians have to take the initiative and step off the curb before traffic making legal turns will stop for them. There are a few major intersections in some cities where even turning traffic is held back by their own red arrow lights when it's the pedestrians' turn to walk. But most of them are not like that. In America it's our sacred god-given right to make a right turn. I doubt that we'll ever have the answer to that question. The fact that it only happened once is a clue that it was a slow process. All dogs are descended from a group of a dozen or so in Mesopotamia right around the time of the Agricultural Revolution, when it would have made the most sense for them to be attracted to our new, much larger middens, and for us to appreciate the help in keeping the place clean. It was apparently much easier and faster for the people who already had domestic dogs to trade or otherwise bring them to nearby villages than it was for the people there to duplicate the domestication process. The same is true of cats; they're all Felis silvestris libica, the subspecies that was welcomed into the granaries of Egypt to feast on rodents.