Some describe it more delicately than others, but it is a common problem and one people find to be very distressing. Dogs like to eat poop. That's really all there is to it.
People find it disgusting, dogs find it delightful.
Still most people want it to stop. I didn't really use much editorial discretion on the subject because I haven't really studied it enough to have a strong opinion. Thus different sites disagree. Dr. P's Dog Training Library - Behav. A simple listing of all the dog-play pages.