The reason is very simple-
Puppy and Cat Mills and Back Yard Breeders must make a profit
in order to stay in business

If you adopt a Pet from a local shelter or pet rescue organization,
you will be saving the life of a pet that deserves a loving, caring owner

Many Pets available at shelters have already been house trained,
Some have even had obedience training
These pets usually have already been given their shots,
Most have already been spayed/neutered

Many shelters have spay/neuter services available at a greatly reduced cost

You can find online shelters in Wisconsin by
clicking on THIS LINK

You can also find pets available for adoption on the
Petfinder Web Site
which has a searchable database of dogs, cats and other pets
available for adoption.  You can even search for a specific breed.