Maybe you missed the whole point. Inbreeding is not for genetic diversity, and most of our morphs are simple recessive, but mostly co-dom. Needing only one generation of mother son breeding to get the homozygous form.
Do you have any specific evidence of genetic mutations caused by inbreeding that you are referring to?
There is still a steady supply of new blood being imported, and most large breeders do indeed out cross, especially with the large number of co-dom morphs with only a normal female needed.
Most pet stores do not breed their own animals, are they are notoriously WC animals. So that theory is bust.