Interestingly, for a currency to actually be useful, there needs to be a demand for it, something that you can only pay for in that currency. For real currencies that is normally taxes. England only accepts taxes paid in pounds, so there's a demand for pounds from every person who has to pay taxes in England. For crypto, extortion is basically the only source of demand.

Sure, occasionally there are places that accept both real currencies and crypto currencies, but for legit businesses almost none of the revenue comes from the crypto side. But, for ransomware, etc. the hackers only accept crypto. That means there's a demand for crypto, which means that it has some value.