Every year 2 to 4 Million puppies are bought from puppy mills, operations that function under terrible conditions. In a puppy mill the bitches usually live their lives in very small cages, with very little to no human interaction, under terrible sanitary conditions with the sole purpose of having one litter after another.
Puppies from these places are often riddled with medical conditions from the start, have no positive association to people and grew up under sub-standard conditions. They often end up in pet shops, or are being sold privately under the disguise of coming from a reputable breeder.
Now the number of pets that are being euthanized in shelters every year is also about 2 Million. These animals are being killed because there are no homes for them. At least that is what we are told. So half of theses killed animals are dogs and there is a demand for twice to four times as many dogs out there. So if only half of the people that shop from puppy mills would go get a shelter dog, there would be no need to euthanize another dog in any shelter.