SUrely, there's some inefficiency in how numbers are used... 10 quadrillion for 7.5 billion people isn't enough?
The main problem is that in Japan everybody has like 5 credit cards, because every big company has its own financial branch and issues cards (maybe to profit from a "reservoir" effect of the accounts?). So you have a credit card linked to your clothes shop, one from your supermarket, one from Rakuten (Japan's Amazon), etc. You get points when you buy things from the company linked to your card. I don't know how it is in US, but it certainly isn't like that in France for example.
This is a fascinating departure from my expectation, because when I was in Japan, I distinctly noticed that credit cards were not accepted everywhere. One could load money into Suica/Pasmo cards and use those at convenient stores, but I learned that carrying cash was imperative -- Japan seemed very much to be a cash-oriented society.
So they are now in the absurd situation where they do not have enough credit card numbers, but still many shops do not accept card payment.
(I edited my previous comment for realism: it's more 5 cards/person than 15)
It's more 5 cards than 15, I admit... I edited my comment accordingly. It still seems a lot to me, why not just one?
We have a credit card for a mall, only for the free parking at said mall. We never actually pay anything with it, only scan it in the parking garage.
That said, cashless transactions have gone way up in the past year though, though the introduction of PayPay QR code payments (which means that waaay more small mom&pop stores accept a cashless payment system since adopting it is basically free), the government 2-%5% cashback cashless incentive that ended earlier this year, and the coronavirus.
It will be interesting to see the new cashless usage numbers next year.
[1] https://en.wikipedia.org/wiki/Payment_card_number#Structure
It still seems like a comfortable amount of numbers.