Do not trash Fiat yourself when it's actually needy, crypto and Fiat must co-exists until the government decides to go digital with Fiat themselves, and Fiat is not trash.
The economy of some developing countries is cash driven. Their financial transaction is mostly through fiat because online transactions are either low or non-existing. In such countries, you need cash to buy almost everything so keeping your money in cryptocurrencies might do more harm than good. Bitcoin can be used as a hedge against inflation or an investment tool but in these countries fiat is king. Government policies also affect the use of cryptocurrencies. Crypto-friendly governments will also promote the use of cryptocurrencies. And from some indications, the Nigerian government is not friendly.