
Only the breeder can register the litter. I rather doubt the breeder just couldn't be bothered (as nomally a registered litter would be higher priced).
I suspect that he was unable to register them for some reason.
Reasons could be the bitch is too young/old.
Had too many litters already.
One or other parent is not KC registered themselves, or have restrictions on their registrations so that pups can't be registered. These are called endorsements and are usually placed by reputable breeders on the puppies they register.
They can be removed, and usually the breeder will do so as long as certain conditions are met, these normally being that the dog is a good representative of the breed and of breeding quality as to temperament and looks, that the dog has undergone Health screening (usually Hip Scoring, and eye testing by specialists, and often also Heart, Von Willebrands, or other genetic disease the breed may occasionally suffer from).