Puppy Mills ...
That is why it is never ever a good idea to get any animal from a pet store, the majority are from those places. It is also vital to always go to the breeders home, and see the parents of the pups. There are so many backyard breeders too, people have to be very aware at what goes on before getting a pup from anyone.
To me it is not a decision to be taken lightly, and one must be extremely cautious as to where a puppy is bought. Yes, it is terrible and absolutely discusting .