Im not sure cryptos really qualify as currencies, or at least efficient ones. High transaction costs, low liquidity, extremely volatile price swings. You want stability in a currency. You don't want to buy a car in Bitcoin, only to have its price shoot up $20k a month later. Or conversely, you wouldn't want to sell a car in Bitcoin and then watch its price drop $20k. These things are just mediums of wild speculation with only a thin veneer of underlying theory to provide legitimacy.