I think that another reason is because of their size. I have always been around dogs that weighed about 35-40 pounds or so. A 40 pounder can eat things that would be harmful to a 6 pounder. Just think, my baby is 8 pounds, and my human baby was 7 lbs., 11 ozs. at birth.
I would not let my newborn sniff the ground or pick something up off the ground and put it in her mounth.
But these little guys are forever the size of a newborn, or smaller. Their little bodies just can't handle what a larger dog can take. Well, that is my theory.
