Pretty sure that's also accounted for, by buying multiple keys. Each person gets their own login, key, duplicate key for backup (placed somewhere offsite).
They don't want you backing up someone elses key on your account. Again; the idea being that each person has 1 of these things. If you need a backup Yubi-Key, they want you to be buying a literal duplicate key; not having your 'backups' on someone elses key.
Have you guys learned nothing about not sharing passwords?
I don't understand why apps and services are so obsessed with 'Passkey' or password-less login. I know there's some risk using email & password login method, but the passkey thing is half-baked and it locks users from getting their account back if somehow they forget it, especially Google's passkey approach is totally awful.
Can you imagine if every company forces users to use Passkey instead of other log in methods, how many printed copies or keys you'll need, plus the spare copies and back-up keys?