Yes, I agree. It’s not a lack of nutrition or anything. Puppies watch their mothers clean up after them in the litter, and some puppies continue the habit. We just had this very conversation with the vet. She said many puppies just grow out of it, but sometimes they don’t.
The best thing you can do is try to break the habit, but that is tough. So, for example, muzzling and then cleaning it up might help break that cycle and maybe eventually would diminish the behavior.