Decades, not years. Size of credit card and debit card has remained the same for over 35 years, if not longer.
Ditto the User Interface of Microsoft Word and Excel since their inception ~30 years ago.
Ditto the home page of Google and Amazon since their inception 20–25 years ago.
While the public discourse heavily glamorizes change, there are many things in the world that have remained largely unchanged over decades but are still hugely popular and continue to dominate the market. Size of credit card and debit card is one such thing.
Others have already explained why there’s no compelling reason to change the size of credit card and debit card and highlighted the repercussions of forcibly changing it just for the sake of changing it. So, I won’t go there.
Instead, I’ll touch upon another thing about credit card that hasn’t changed. That’s its basic functionality. When credit card was launched 40-50 years ago, its was meant to provide a way for a random consumer to walk into a store, pick up something and leave without forking out cash, even though the cardholder and the merchant didn’t know each other from Adam. That continues to be the basic purpose of a credit card even today.
Over the decades, several alternative payments have emerged e.g. Account-to-Account Real Time Payments (e.g. FPS in UK, Zelle in USA), Carrier Billing / Gen Y Mobile Payments (e.g. Boku, Zong), ACH and ACH-alternatives (e.g. Dwolla), etc. None of them has managed to make a dent on the popularity of credit card, despite the fact that not just the shape but even the functionality of credit card has remained unchanged during this period. Credit card continues to be the most widely used cashless method of payment in the world.
Once in a while, a product is invented that’s so future proof that it keeps working for decades without any fundamental changes.
Credit card is one such product.
UPDATE DATED 8 NOVEMBER 2019:
I’ve been asked why I didn’t mention Apple Pay, Google Pay, et al in the above list of alternative payments.
The reason is, all of these new payment apps work on top of the credit card account and use a credit card, just in a different form factor. Instead of denting the popularity of credit card, they have, if anything, increased its appeal, if not also its reach.
The moment I mentioned form factor, I realized that’s related to shape and size. Instead of plastic, these apps use mobile phone, smart watch, wearable band, and key fob to store credit card details.
Which means, the size of credit card has changed.
These new form factors of credit card are still very much in their infancy. Credit card, in its traditional shape and form, still reigns supreme.