It could be that he is eating too fast and the poop has undigested food in it which attracts him to it. Or, he saw mom eat puppy poop and wants to be cool like mommy dog. But rather than worry about 'why' - put a tablespoon of pineapple in his food it makes the poop unattractive to them
Your puppy is likely not getting enough food at each meal to satisfy him therefore he is left hungry enough to eat his own poop. I suggest increasing his food.
Usually there is food left in his bowl after he is finished. We do feed him 3 times a day plus a couple treats at different times so I don't see how he could still be hungary.
Wendy, my old lab used to do this all the time. The vet gave me something to sprinkle onto his food to make the poop taste bad. Yep, that's exactly what I thought, it doesn't already taste bad????? I think you can actually get the stuff at PetSmart now, I'm sorry I do not remember what it is called. I also had to put in my other dog's food, because he enjoyed eating her poop too!
Motta and Miley have stopped eating poop except for rabbit poop now!! UGH!! (they haven't found the litter box yet) I guess rabbit poop is better than their own though :) and soon I am sure they will have chased all the rabbits away which would be wonderful!!