It's the way the credit system was designed, even before widespread computer networking - based entirely on trust. The customer would bring the card in and the merchant would make a signed carbon copy and call it in or deliver the receipts to the bank every day, which would settle the accounts between banks over a week or so, with the credit card provider carrying some level of liability. This is one of the reasons credit cards weren't accepted most places until networked POS terminals and instantaneous verification made the trust more practical.
Some merchants have their own verification steps in addition to the terminal like Best Buy checking a customer's ID to see if it matches the card and one of these special cards wouldn't fly if anyone actually looked it. It's not like you can walk into a Lamborghini dealership with one like you can with a Centurion card (which has some sort of concierge service for verifying large purchases IIRC).
