You are correct, however, the temptation to breed a morph or pattern is tremendous when you have limited individuals expressing the desired traits.
Look at the caramels with the kinks. I don't recall the guys name who had the video of them, I am terrible with names, but if you listen to him he never says he won't ever breed them.
The temptation is too much for whatever reason. Had he culled them, there would be NO possibility of their further contributing to an already weak genepool.
Same thing for the one eyed boas. kahl sold many many siblings without disclosing that little fact. Now lots of breeders have that defective gene. The good ones cull the one eyes and breed different adults next go round.
Sterilization would work as well, but I don't know of it being done with snakes.