The bank/exchange/etc that was entrusted to protect your dollars/bitcoin/etc. FDIC insurance is indexed to dollars but insures the value of your deposits. If

The bank/exchange/etc that was entrusted to protect your dollars/bitcoin/etc. FDIC insurance is indexed to dollars but insures the value of your deposits. If someone robs a bank there is no way to reverse the robbery by invalidating the physical assets they stole be it cash, gold, bitcoin keys etc. This is not a problem most cryprocurrenties propose to solve.