I agree assets with fixed inflation, be them cryptocurrencies or precious metals, make poor currencies, but some cryptocurrency projects are actually working on algorithmically price-stable currencies (ie. a cryptocurrency with a dynamic supply, not pegged to another fiat currency).

When/if the supply problem is solved, and a more environnementally friendly consensus mechanism than PoW developed, there won't be many arguments against adopting cryptocurrencies as the default payment method.

[1]: https://debaseonomics.io/, https://reflexer.finance/