The vast majority of crypto transactions are speculation: Hoping somebody else will be willing to pay more later. (The "bigger fool" theory.) The next largest class of crypto transactions is illegal commerce, from drugs to ransomeware (which really only got big when crypto made collecting ransoms easy) to human trafficking. A minuscule part is legitimate commerce, where someone who either bought it as a speculation, or bought it in a misguided belief that it would actually be useful, spends it at one of the tiny number of merchants who accept it and immediately convert it back into real money.
It is useless as currency because its value is wildly unstable, and it offers no protection for consumers in cases of fraud. It produces nothing of actual value. Money is useful because in an industrial economy barter doesn't work. We need a medium of exchange. But for the medium of exchange to be useful it has to have a relatively stable value and it has to offer some protections against fraud, neither of which crypto does. Even so-called stable coins end up going bust because they're not actually backed by anything. US. dollars are backed by the government. Stable coins are backed by fly-by-night businesses operated out of somebody' garage.
