the AKC doesn't care if you sell dogs without papers. However, if you advertise your litter as "$400 with papers or $200 without" the AKC considers that to be "selling papers" IE, you are charging them $200 just to get the AKC registration.
That is illegal under the AKC. If the dog is worth $200, then AKC paperwork isn't going to magically make it a better dog. It is their attempt to help stop people from ripping off buyers. Selling pups for different prices with or without papers is a huge red flag of a bad breeder.
There is also the fact that AKC papers can be stolen. Maybe. Litter is registered and a pup dies, but the paperwork remains. Someone unethical seller can use that paperwork on a different dog to try and increase its value or appeal to a potential buyer. Some backyard breeders even register more pups than are actually born in order to do this. It is why DNA testing is becoming so important in dog breeding.