Some Petsmarts don't carry them. Our local one does, though. I'm sure it's just up to the individual store manager.
Store managers do not have that kind of power, its cooperate. It could also be that only test stores carry them.
They have certain stores test out how well animals do, or any major changes do, in a working store setting.
One of the stores was trying out cockatiels to see if they would be a good fit with the stores.