Since the formation of motorways, some people have lost the instinct to read maps. Then there might be another reason, that they believe motorways have a far better chance of being cleared throughout the full length, before any other routes. All pure speculation of course!.
Perhaps going off subject, but around our way the conditions haven't been really bad. Not far from where I live is a major road which leads to motorways, so that road is very heavily used. Yesterday someone noticed a motor vehicle down the slight embankment, upon checking there was a young male in the wrecked car dead, apparently he had been there for four days without anyone noticing that there had been an accident. The irony of that, was the fact that the police headquarters is a short distance up the road, and police vehicles are constantly using this road, yet no one suspected anything.