Yep, this is something I never understood myself when I worked at Petsmart. They treat their animals lousy and cram way too many into a single enclosure...yet they refuse to sell any mammal as feeders or even breeders! They have 'pet contracts' that customers have to sign stating they won't mistreat the animal...which is rather pointless. I had no problem selling rodents to people I knew were using them for breeders or snake food, and I just warned them not to come in to any one store too often to do that. If they wanted to spend that much (mice are $5 a piece, rats $10) on feeders I wasn't about to refuse. However, I seemed to be an exception.
Good luck.