First off, it is a problem with enforcement. No one is getting ticketed for it.
Second off, it is just another example of the lack of concern for others that is running rampant on the road today.
While this annoys me, there are some companion behaviors that really get me going.
"Driving by the buddy system" - Two lane road, two vehicles side by side, both at or below the speed limit, maybe just above it. This is especially not fun when the vehicles are semi's.
"The blind spot hangers" - They come up behind you while you are in the right lane. get their hood just by your left rear tire and stay there.
Of course none of them are getting pulled over by the cop talking on his cell phone while cruising.