They don’t. They could maybe. But I want an easy solution to transfer money to people and pay online. Crypto is not that solution because I cannot pay with it in most online shops and I cannot send money directly to other people. The money has to be exchanged to some arbitrary other currency.
Unless everybody used crypto as their main currency and everybody used the same cryptocurrency at that, it’ll always be an extra step, subject to fluctuations in exchange rate and possibly fees/taxes. As long as that’s not the case, it’s not an alternative. So yes, it’s an adoption problem but one that isn’t realistically solvable any time soon