Okay, back up a little. Crypto miners mine crypto in order to become rich. With national currencies, this is impossible. Citizens cannot create their own currency, and that's a good thing. If money could be easily forged, it would either be worthless, or a speculative instrument, like every crypto in existence. National governments are the source and the only legal creators of money.

Crypto mining also makes the blockchain secure. What this means is that a malicious individual cannot, say, transfer crypto from another person's wallet to his own, or alter the software algorithm that controls the creation of the cryptocurrency.

Proof of work cryptocurrencies require miners to expend an enormous quantity of energy in order to prevent problems that national currencies don't have in the first place. Cryptocurrencies have no advantage over national currencies except for anonymous online transactions.