Dogs are much harder to unload than ball pythons, because there is such a surplus of them around. Anything imperfect and less-than-show-quality is just as hard to find an owner for as dogs at a shelter. Unfortunatly since these breeders make a business out of it and compete in a world with such surplus, culling is the financially logical option. This is partly why I will never buy from dog breeders, even the good guys of the business who don't cull and take good care of the dogs.. Supporting part of the business helps keep the business as a whole.

Ball pythons, even normal males, are pretty easy to find homes for(even if you don't make much or any $ out of finding that home) just about anywhere in the US, and I don't know anyone who culls based on anything other than deformities that impact an animal's health, though I have heard of it happening.