Why Credit? Because a Debit is used for Debt and sounds too much like Debt. Accounting terms can be used. Anyway Credit cards would get a whole new meaning. You earn money to insrease your credit, thus the name credit can be used on the Global Currency. Sort of like a Smart Card, or pre-paid credit card.
This term is used in Traveller, they use the word Credit for their unit of currency. All planets take credits, and it's value is determined by the universal stock market.