So do puppies. Babies don't have to be walked and run after eating. They just need burping. Babies need daily baths to smell sweet. Babies don't get fleas.
Puppies can and do.
Puppies don't let you sleep and tea and cookies at 3AM don't help you out either. You can loose weight running an older dog, not a puppy. Babies grow out of their clothes, fast. Puppies outgrow their collars. Babies chew up the furniture.