In short, people who have purchased puppies whose breeders were more interested in the bottom line of making money on puppy sales rather than the overall health and welfare of both the puppies and their future homes. Unsuspecting people purchase these innocent puppies. Raising puppies who grow into mentally and physically healthy dogs is a tremendous undertaking, not one to be taken lightly. People who make money are cutting corners, which is extremely irresponsible. Many people aren't even aware what constitutes responsible breeding, others just don't care.
Responsible breeding starts with selection of the parents.
Having AKC papers and a pedigree stating the parents are purebred is NOT enough. The parents must meet the criteria of conforming to the breed standard and be superior specimens of the breed. The prospective parents should be screened for a variety of inherited health defects, including heart defects, eye defects, hip dysplasia, luxating patellas, bleeding disorders, to name a few. The breeder should be fully familiar with possible problems existing in the pedigree and bloodlines, such as epilepsy, excessive fear or shyness, aggression, etc. Parents should be paired because they compliment each other's strengths and weaknesses, not just because they belong to the same breed and mating those two dogs is convenient.