All the bits and such to generate those passkeys originate on one device... And it's specifically designed for it's security, to not allow the key material be removable from that one device...
A device that may end up in the bottom of a canal in Venice...
It's then a case of how do you bootstrap back up to having access?
- Did you remember to spend money on an additional passkey device? - Did you ensure you don't need the passkey device you lost to access the other device which the passkey syncs with (for the iOS keychain/google whatever options) - Did you remember at each. and. every. account. you. have. to enroll both your primary and secondary passkeys?
vs.
- You can remember enough to get into email for resets, or there's a note or a thumb drive kept in a drawer that has enough password info (itself possibly password protected) to get you back on your digital feet.
I understand the need for not being able to export from a passkey device... but it massively shifts the paradigm of how users need to operate. And puts all the trust in devices.