Bro, the people who deposited their gold in bank vaults weren't the middle classes. Paper fiat was not simpler, easier to verify, or easier to store/transport than gold or silver. So much so that for millenia most people refused it. States wanting to issue fiat had to make do with minting debased / plated precious metal coins. Partly-fiat and partly-metal. Britain's currency is still called the "Pound" (of silver, once). "Dollar" is an anglicisation of the Dutch "thaler", itself from Arabic "Dinar". A very specific gold weight coin.