[...] people think they must only have one.
That's the real failure? I think the real failure is that people must have _more than one_. I thought so hard to add all my credentials to 1Password. Now people tell me I should use a Yubikey (or better two or three of them). What do you think, I'm going to register a couple of hundred accounts times three for something I already have (my password manager)?
The real advante in passkeys is in allowing me to log in into a service on a foreign device without typing [my password], which is (honestly) something now sane person should ever do.