> they're precisely the same difficulties people have moving from the paradigm of "memorizing or writing down all my passwords" to "using a password manager."

Errr, no.

You can transfer a password from one manager to another. Those very same password managers won't let you transfer a passkey they hold.

And if you know the password, you can use it anywhere by just typing it in - no complex technology or protocols involved. But using a passkey involves your secure computer talking to another computer, using a complex protocol that can't go via eyeballs and fingers. If you don't have a way to connect the device holding the passkey to the computer wanting your id - say your USB A Yubikey isn't recognised by your phone, then you are out of luck - you can't use that passkey, even though it's sitting in your hand.

And you can't work around that by copying the passkey to a device that can communicate with the service you're using, because you aren't allowed to copy.

It's an unworkable mess. The mess is not created by passkeys themselves, because, as others have said elsewhere the protocol is pure elegance. The mess is created by vendors choosing lock in over transportability. I'm hoping it's a passing phase.