My experience is that even registered ANKC breeders can sometimes morph into puppy mills of sorts. I got a dog from a registered breeder and was very happy with her. Some years later I went back to the same beeder and they were pumping out 150 pups a year and had stopped showing their dogs, no health testing. I got a pup and she was diagnosed with ED at 9 months old and had a very dodgy temperament. Meeting other people with some of these dogs I started to realise there were all sorts of issues such as PRA etc.
The dogs were not uncared for and were healthy etc but they did live their lives in a kennel complex and there were a lot of breeding dogs. The breeder continues to breed from 2 of my dogs siblings despite a couple of us having ED pups from that litter. Several people complained to the ANKC but got brushed off although I think they did send a letter noting the complaints to the breeder, but it made no difference.
So my next dog a BC I did a lot more homework and found a good working dog breeder. I went through lots of hoops to get one of her dogs and he has turned out to be a beautiful working sheepdog. Nothing to do with ANKC obviously but from top UK ISDS and Australian proven working lines. She stands by all her dogs and I have got to know her really well and she continues to take an interest in the progess of my young dog.
As to people buying pups from pet shops, most of my acqauaintences do this. I do try and point out why they shouldnt but it falls on deaf ears - they simply have no comprehension. There is probably a stage in my life before I knew so much more about dogs where I would have done the same.
Nowadays I tend to go to working dog rescues and see what they have to offer and I have a wonderful Koolie and a Kelpie from rescue in the last 6 months.