I share your concerns, but you can store passkeys in the password manager of your choice, which syncs them across all your devices. As long as device attestation remains optional (and that's a big if), passkeys are strictly better than passwords.
Exceptions for hardware-based solutions (like Yubikey) are acceptable and reasonable, as long as there is a ban on implementing any attestation anti-features.
Current spec and official demo sites doesn't even require or suggest that multiple Passkeys must be a thing. A significant number of actual real-world implementations are extremely user-hostile (check BestBuy for an example).