Before then (1931 for the pound and 1933 for the dollar, though they maintained de-facto parity with gold until 1971), dollars and pounds were considered good investments. That's why we had bank runs: people thought their money would be safer under their mattress, and preferred to own physical currency rather than numbers in a bank's ledger. The only reason holding USD is a bad investment is because inflation is basically guaranteed: you know that a dollar will be worth less tomorrow than it will be today, because the authorities that control the dollar say so. Not so with Bitcoin: the total supply is fixed at 21M, forever, and there's no central authority with the power to change that.