None of what you’ve mentioned has anything to do with Visa and Mastercard. Visa and Mastercard are just payment networks, their whole business is literally just transporting transaction information from payment terminals to banks and payment processors, plus keeping track of all the numbers (which is pretty important).

Payment networks don’t provide credit or any kind of liquidity whatsoever, that entirely provided by the various financial entities that communicate via the payment network. The reason Visa and Mastercard haven’t been easily replaced is simple network effects, nobody wants to integrate with a payment network where there’s nobody to transact with.