That's the "cover story" use case. The real use case is so that passkeys created on Apple devices can only ever move to other Apple devices, and ditto for on Microsoft or Google devices, and the real point of attestation is so that they can force you to use theirs by cryptographically ensuring that you're not using open-source ones like KeePassXC.
As an example, see this issue opened against keepassxc saying that if they continue allowing plaintext passkey export, they're at risk of being blocked once attestation is standardized:
The goal here isn't maximizing user choice, it's to enforce minimum agreeable standards by the major vendors. It's up to you whether your personal needs wholly align with what they want to mandate, forever.
