Safes on Statendam, Maasdam, Ryndam and Veendam all require the use of a magnetic strip card. What's the big deal? I use an old department store credit card from a store that is out of business. That allows us to lock all our valid cards in the safe.
The key card cannot be used for safey reasons. Your name is on your ship's ID card and if lost, it is conceivable someone finding it could learn the cabin number and use that card.
I don't see any big deal about using a separate card for the safe or reason they should have wasted money converting perfectly good safes into a keypad system. Be creative. It isn't like you have some heavy key ring to carry. It's a slim credit card. If you don't care to carry it, be creative about finding a place to put it in your cabin. There are any number of 'safe' places to leave it in your cabin.