The big problem here is you've no fall-back for when the place you're trying to pay, or their merchant services provider, has a communications/network outage or malware attack or has assets frozen - some of which affect multiple large retailers.

There have been many instances over the years, even just in the U.K., where small and large stores have been unable to accept digital/network-required payments and ended up with massive queues or customers abandoning shopping carts full of items due to not having cash.

"Spar cyber attack hits more than 300 convenience stores" (2021-12) https://www.bbc.com/news/uk-england-lancashire-59554433

"Manx Telecom broadband outage affects 4,000" (2020-08) https://www.bbc.com/news/world-europe-isle-of-man-53920785

"Wirecard: 'It’s really bad. I’m left with nothing'" (2020-06) https://www.bbc.com/news/business-53222181

"Debit card glitch means thousands charged twice" (2018-09) https://www.bbc.com/news/uk-england-45400234

"Visa (Europe) says service returning to normal" (2018-06) https://www.bbc.com/news/business-44335804

"Asda card machine fault leads to queues at checkouts" (2016-10) https://www.bbc.com/news/uk-37815973

"RBS says it has resolved debit card computer glitch" (2016-10) https://www.bbc.com/news/business-37658559

"Lloyds Banking Group says card problems sorted" (2014-01) https://www.bbc.com/news/business-25907000

"Card payments system crash disrupts shoppers" (2010-10) https://www.bbc.com/news/uk-11458962

Also, interesting and somewhat unexpected contactless from long distance!

"Contactless 'charging errors' at Marks and Spencer" (2013-05) https://www.bbc.com/news/business-22545804

And there's no fallback for when you have to make multiple payments and don't have the cash on hand already. There's no fallback for an ATM outage where you can't withdraw the cash. There's no fallback for a communications/network outage at the bank where they can't query your balance and withdraw funds for you.

There are problems with any system. This one has the advantage of convenience.

Ok. But it's the rare instance where I can't postpone my purchase until the system comes back online, or just go elsewhere. I can't remember the last time the US had a nationwide outage like that. Maybe an individual store but not the entire region.

I keep an emergency $20 on me going back to the early 1990s but I've only ever needed to spend it once in almost 30 years.

Or the store just has to close entirely because they "can't" accept cash.