We had originally planned to go all-in on passkeys for ONCE/Campfire, and we built the early authentication system entirely around that. It was not a simple setup! Handling passkeys properly is surprisingly complicated on the backend, but we got it done. Unfortunately, the user experience kinda sucked, so we ended up ripping it all out...
The answer to all of these questions is “For the exact same reason they do all these same things with passwords”
Think of a passkey as a very, very complex password that is stored on your device (or in a password manager) that you can use to log into websites with without ever having to know what the password is, and it’s never stored on the site you’re logging into, even in a hashed format, so it literally can’t be exposed in a breach.
It’s the exact same technology you use to connect securely to every website you visit, except used in reverse.