Comment by WorldMaker

Backup and syncing has indeed been mentioned many times as a factor by Apple why they don't think supporting attestation for consumers makes sense. Consumers need easy/automatic backup and syncing for these keys to be used at all in the consumer world by non-technical users. It is the "it just works" of Passkey management.

Apple has also made it clear they have privacy concerns about attestation as well, which is also why they don't support it, but backup and syncing are clearly very important to Apple because that is very important to keeping consumers happy.