I mean let's face it, it's easier to handle money electronically than with papers in the hand. And if we compare fiat on the bank account and the blockchain money guesses who have the advantage...well not quite yet, but the potential for the blockchain is huge.
It is not always more convenient to work with electronic money, although in some cases they are better than fiat. These two types of currencies have their advantages and disadvantages in use and will only go together. Cryptocurrency will never replace the national money of states. Cryptocurrency can not interact with the economy of the state, as national money does. In addition, the cryptocurrency has a high degree of volatility and, due to even these two reasons, it can never replace the usual currency.
Fiat currency has been there for more than a century and still it is working. You cannot call it a failure so easily and it will not be completely eliminated. Digital currencies are better and good but not everyone is at ease using them. Also you need technology to be able to use them unlike fiat which even an illiterate person can use easily.