I have a Sams Club credit card that has the chip & PIN feature. They state that the PIN is required when using it at Walmart and Sams Club, but I have used it

I have a Sams Club credit card that has the chip & PIN feature. They state that the PIN is required when using it at Walmart and Sams Club, but I have used it in other places and have had the transaction go through with or without a signature (the latter of which was for a purchase under $50). Do the terminals have an order of preference in terms of what's required for payment. For instance, try chip+pin first, then try chip+signature, then try mag stripe+signature? If that's the case, then I don't see why all stores that have chip readers won't start using chip+PIN as a first preference for payments with chip enabled cards.