Mastercard is a payment support platform. They take the burden off of the business owners and let them focus on their business instead of the minutia of interfacing with the financial system. That doesn't go away with cryptocurrencies. In fact it might be more needed than ever as there are now multiple payment networks with lots of intricacies such as coin storage, keeping track of transactions for taxes, etc.
Visa and Mastercard are likely still going to be important in the future just for the sheer fact that business owners will take at least a decade to update their backend stack to be sophisticated enough to handle the various payment APIs, UX problems, etc that crypto brings. With Visa and Mastercard your existing PoS terminals still work (now with crypto) and you can continue focusing on selling books or groceries or whatever else you do instead of being a financial systems engineer.
That's from an end users perspective. From a merchant's perspective if they provide that QR code they now have the additional burden of custody of a bunch of crypto assets which means learning about, installing, making a specific bank account to sell the coins, dealing with tax burdens, etc which is a lot of work and risk for someone already overworked and stressed by their primary business.
Or they can just use a payment network like Visa or Mastercard and not have to worry about any of that. You pay with BTC or ETH and the merchant receives USD. Everyone's happy. The merchant doesn't have to hire an additional crypto-specialized IT person or spend 6 months diving down the rabbit hole like we did. They just run their business.
Yeah and those accountants charge by the hour. Crypto taxes take up a lot of hours (and that's if your accountant already knows how to deal with crypto). The vast majority of small businesses don't have dedicated accountants and having to pay for the overhead of dealing with crypto is not in their already strained budgets.
Visa and Mastercard are likely still going to be important in the future just for the sheer fact that business owners will take at least a decade to update their backend stack to be sophisticated enough to handle the various payment APIs, UX problems, etc that crypto brings. With Visa and Mastercard your existing PoS terminals still work (now with crypto) and you can continue focusing on selling books or groceries or whatever else you do instead of being a financial systems engineer.