Too many services don't allow multiple passkeys per account. If they are supposed to be device level attestation, you need to be able to enroll one per device. I know that there are some frameworks to connect an enrolled device to attest, but that a) plain doesn't work well for some configs, and b) is annoying. I understand having a hardware security key for some stuff, but I feel like having that be a random ass phone for most people isn't really that desirable.

I feel like syncable passkeys are a band aid on top of most services having no idea how to implement passkeys well.