Sure, a standard exists, but that by itself isn't a great user experience. If you actually try to use something like a YubiKey you end up having to register multiple keys with each site to deal with lost key (assuming the site allows that in the first place). The you have to remember which keys correspond to which sites, and remember to get your backup key out each time you sign up somewhere new , etc.
Google, Apple, etc are building on WebAuthN in order to allow a trusted third party to "sync" the keys, solving the major usability hurdle for most people (as with all things security related, there's an obvious tradeoff in injecting a trusted third party, but for the vast majority of people that tradeoff still results in a significant net risk reduction). I assume Bitwarden is angling to build out their own version of something in this space.
I'm probably more excited about passkeys than most, but I don't see why you need $100M to add support for that. It's a pretty straightforward addition to existing password managers. Might even be easier to support than it is to build a user-friendly password autofill, all things considered.
I find that the essayist way to handle backup keys is with a printout of 10-20 pre-generated auth codes, which go in my safe. Much easier than having a backup hardware key I have to remove and then replace from my safe, each time I need to add a new service service.
Which is great if you have a printer (and are near it when you're signing up for the account, and remember to do it, and remember to put it in your safe, etc...). Just because it's the easiest way currently doesn't mean there isn't substantial room for improvement in the usability of passwordless systems. Most users aren't going to go to the trouble of printing something out like that.
Hasn't really caught on, despite being several years in the making already