Why Fiat? As I can see cryptocurrencies are already failed most in the history too many scammers and hackers trying to breach the system or exchanges, fiat can trace I guess and hacking also are involved here.
In the current era, particularly in developing countries, fiat is the most successful currency for it has a huge demand and is widely used as cash and to make instant transactions.
On the other hand, cryptocurrency is not a failure as well. In developed countries, it has been used as a medium of exchange and to save and store value. However the market is down right now due to many reasons but both the forms of money are of great use and importance.