Unfortunately, there are too many puppy mills out there.
But you also have to consider the difference in customer base difference as well. A person purchasing a puppy from a breeder does so because they want a specific breed of dog, along with the bragging rights that their dog is a purebred animal of such and such lineage. The dog may become part of the family, but often becomes a show dog. Or a hunting/working dog. When it goes right, the animal has the best of both worlds.
Rescue animals, on the other hand, ate not purchased, but adopted. The people that do so don't give one whit about the dog's lineage. They might be partial to one breed, and will try and find one that comes close. Or just a pup that will be their friend or a companion for their child(ren). Our boxer was my best friend during my childhood. These people are not looking for a perfect dog, by breeders standards: they are adopting a new family member, giving a chance to an animal that still has a lot of love left in them. Believe me, I've seen three legged dogs that were ad active as four legged ones. They loved their owners whole heartedly. There owners loved them just as much.
No, for the dog breeder, what they need to do to move their animals, is to advertise on the trade magazine. The rescue dogs are not their competition.