@BeAware Assuming a non-volatile, inflationary currency, if someone wants to earn interest, they'll have to put it into a bank, and the bank can use that money to issue loans.
If currency is deflationary, sure, everyone will put it under their mattresses or in the case of crypto their wallets.
But a deflationary currency would be a disaster for the economy. The great depression is the most famous example of what happens because of a deflationary spiral.