Fiat has successfully existed for many years in parallel with Mastercard/Visa plastic cards and the same situation will be with cryptocurrencies, Fiat will exist in parallel with cryptocurrencies. There are different niches for which their own currency is better suited. The wallet is tied to the phone, and the phone needs internet and if it is not possible to withhold payment using cryptocurrency, then you can always use Fiat currency. Nowadays, plastic cards are not accepted everywhere, for example, in rural areas or in third world countries.