[carlosjobim]

There is no standard because there are different currencies in different empires and different rulers of those empires. Asking why there isn't a unified standard is the same as asking why there isn't a one world government.

The economic burden of the "old-school" payment networks Visa and Mastercard is very low for both merchants and customers for what these networks provide. The economic burden and other burdens of a one world government would be immense in comparison.

Please remember that most people use other methods to transact larger amounts, so the fees are mostly for the convenience of small remote transactions.