There's a great divide between perfectly functioning economy and using ammunition as currency. Something as simple as a broken fiber optic cable, or a small scale war, both could be considered catastrophic (particularly if electronic payment is impossible) while still allowing people to go about their daily lives. But in those daily lives they can do no commerce, rendering the situation much more catastrophic, whereas if they had cash, they could buy groceries and dodge shells on the way home to read a book.
