Why can't this be done with existing public key cryptography?
For better or worse, there are a large (and ever growing) number of Metamask users these days...
The point still is that logging in with public-key cryptography is not exclusively a technology supported by cryptowallets.
I would argue that the biggest successes of crypto are selling GPUs and facilitating malware ransom payments.
GPUs have sold like crazy and you are lucky to get a high end one with the current demand. Everybody and their pets are running mining rigs. Good luck getting a nice GPU for machine learning or graphics rendering.
Previously malware authors had to rely on gift cards or similar means to get paid. Now they have variety of cryptocurrencies to choose from and they can even trade cryptocurrencies to launder the paid ransom funds.
Is it? U2F is actually rolling out to more and more websites but I've never seen any website offer to log in with a dropdown for cryptocurrencies
It’s literally titled “ Real Problems That Web3 Solves, Part 1”