DAMN YOU CLAY!! YOU'VE SCREWED UP OUR ROADS! There, I said it. I've also heard that he's Obama's half brother, but hung like a white-guy.
Probably the closest to the true reason our roads suck. The clay is hard as a rock when dry, and soft as fresh snot when wet. Of course there is also the problem of shrinking to 80% of its original size when hard and swelling to 120% of its original size when when soft.