Why are field bred Golden Retriever puppies so much more expensive than field bred Labradors?

I noticed that, on average, field-bred Golden Retriever litters out of parents with advanced hunt test titles are much more expensive than Labrador litters from similarly titled parents.

Are the puppies from Golden litters more expensive because there are fewer Golden field breeders or because there are fewer Goldens than Labs with advanced field titles? Or another reason?