“Stripped to its fundamentals: a payment is a message, with new information, about a debt, with a certain confidence level associated with it.”
Most money in the economy already moves bank to bank. Most payments still go over card rails that take a cut. India’s UPI offers instant, nearly free, nearly irreversible transfers, and it competes mostly with cash. The US has nothing like it, and the people collecting interchange are in no hurry to change that.