It’s one more brick in the wall preventing general-purpose computing. Want to authenticate to Banana Computers? Well, you have to use one of their oDevices, because they will not let you use a RoboPhone to store your passkeys.
And since any solution excluding either of these is a non-starter, ironically the passkey push has made WebAuthN more open when it comes to client choice.
So while I agree that Apple and Google not allowing passkey exports (yet; I am cautiously optimistic that they'll eventually be pushed to offer that too) runs the risk of locking in non-sophisticated users, the future is looking very bright for everybody posting here at least.
Show me a widely available service that filters authenticators based on attestation attributes?