Unlike consumer or durable goods, central bank money does not have any consumption or utility value. And the issuing central bank’s credit quality and integrity is reflected in the value of its currency. The value of a currency, then, hinges on trust in the central bank.
Not just that: the issuer – so in the euro’s case, the Eurosystem – takes collateral from its monetary policy counterparties as a “deposit” for providing euro currency. That indirectly anchors the euro in the real economy. Virtual currencies, by contrast, have no issuer, no footing in the real economy. No one has to redeem them.