They also only consider registered breeders because more often than not, the animals from backyard breeders aren't up to standard. Even though there could be hundreds of an animal from local backyards, most of them are going to be bad quality and some are downright mutts. For example: The Khaki Campbells from TSC all have yellow beaks, because they were mixed with mallards. The Pekins in this area aren't real Pekins; their beaks are white instead of orange, and they never reach the full size that a true Pekin is supposed to get. Most of the Blue Swedes I have managed to find all have defects from excessive inbreeding; club foot, twisted beaks, etc.
Registered breeders are usually trying to keep the quality of the breed intact, especially if they are registered with the Livestock Conservancy.