That security key works fine in an office environment, but becomes a lot more annoying on, for instance, a mobile device.
[0]: https://www.macrumors.com/2019/11/12/ios-13-3-fido2-security...
So then you don't need the token because the platform (ie your phone) does the multi-factor authentication itself. In this case you touch a fingerprint reader. I can hold my phone in a way where my right index finger naturally is placed to do this so it feels pretty convenient.
Again, not on iPhones today but it has been demo'd and does already exist on Android.