How is cash not decentralized? I can pay anyone anywhere for anything and I don’t need any centralized infrastructure.
The issuance of gold is decentralized. The issuance of cash is centralized, unless you believe in counterfeiting. However, the transacting and storage of both cash and gold are decentralized.
The centralized issuing authority can decide overnight to make the cash worthless. This happened fairly recently in India, for example.