Because 1) blockchain is far more secure than the older methods of xfer, 2) blockchain is faster than the current methods, and 3) blockchain is cheaper than the current methods.
I work with a few banks who are actively using this already and others who are developing the technology. Not sure where you get your information, but I can tell you first hand that banks and credit card company absolutely are using crypto right now.
So Mastercard is not doing blockchain, but plenty others are. https://www.finextra.com/newsarticle/44961/hsbc-and-ant-international-laud-results-of-blockchain-based-tokenized-deposit-transfers