Debit cards are far more confusing as you can spend money that you don't have with them, use them online, over the phone, in person, etc. etc.
You can also have payments that are akin to having a direct debit. e.g. a subscription to pay for internet access that goes out automatically each month but specifically through your card.
Much more confusing than just going to a cash machine with a cash point card and getting a tenner.