At the Petsmart I work at we were told it was for the safety of the snakes. Since feeders can cause harm if they fight back. Not to mention that Freezing the rodent will kill any parasite that it might have.
I think the company as a whole sees it as more of an ethical thing though since the only live feeder animals we sell are fish and insects.
We're not even supposed to sell the ghost shrimp to people that plan on feeding them to fish lol...

I don't see a moral issue with it though. I have just heard too many horror stories of prey injuring a snake. I plan on switching mine over to F/T once she is eating normally for me.