Cash does need a network and constant checks and balances for foul play. You need trusted cashiers, need to check every received note to see if it's genuine, t

Cash does need a network and constant checks and balances for foul play. You need trusted cashiers, need to check every received note to see if it's genuine, then you need to safely deposit that somewhere, the boxes of cash have to be transported likely in an armored truck. And you still need communications networks for all the checks and balances and automated systems to handle the cash. It's a massive logistic effort to shuffle around little certificates of value.