Apparently, a lot of people are plainly and abjectly ignorant of the law. Maybe that is partly the answer.
http://fredericksburg.com/News/FLS/2008/072008/07312008/397867
This guy thinks that left lane passing laws are "new", and he cannot understand why he can go 70 and some other person can't go 75.
When he asks "As I understand this new law, if a more impatient driver comes up behind me, I am now authorized, by law, to speed up even more just to satisfy this other driver?" I almost want to figure out how to contact him so I could tell him that I once did just that, knowing full well that a cop was driving in the far right lane on a three lane stretch, obscured by a tractor trailer. I sped up, moved into the middle lane, saw the cop speed up after me, and then when the guy behind me zipped by, the cop went after him, not me.
Plus, 90% of the cops will let you go with only a warning if you tell them you were speeding up to pass a row of slow moving cars in the right lane because you were trying to get to the upcoming exit.
And if you are on a two lane road with a broken yellow line with a 55 mph speed limit, and you want to pass a car going 50 mph, you obviously have to speed up well above the limit in order to safely pass the car. I don't think any cop would pull you over for getting up to 65 or 70 just long enough to pass a slow moving car on a two lane highway (unless of course, he just needs an excuse because he suspects you of something else.)