I think a lot of the problems with poor drivers is a result of the increase in freeway/interstate usage. When there were mostly 2 lane roads with a smattering of 4 lane/limited access roads, drivers had to pay more attention to their driving because there was just more opportunities for things to happen, and less places to move to avoid them.
With the proliferation of freeways/interstates, drivers have become more removed from the actual chore of driving, and now are more relegated to steering. Now you have 2 or more lanes to move around in and no traffic coming directly at you. It seems to lessen your involvement in the actual driving of the vehicle.
I see this on the 2 lane roads around here when people will slow down or make a sudden move when there is an oncoming car, after an interval of no oncoming traffic. They just seem startled by the whole affair.