Ha ha, yeah, you would think it would taste yucky! But for some reason the food doesn't digest all the way and to a puppy it still smells/tastes like food to them. EW.
When my puppy came to me she was on Eukenuba and after I switched her to Canidae and used the Forbid for oh, about a week and a half, the poo eating stopped. I tried the meat tenderizer trick first and it didn't work for me. But it's pretty common if you do a search on YT for 'eating poop'