Using a good old password means you don't rely on any particular service, period. Passkeys means you do, you rely on either a particular type of device (e.g. Apple device) or a SaaS.
It doesn't matter how many SaaSes offer it or how many brands of devices adopt it. It still means that for access to all of your accounts, you either 1. Have to stay with that brand of device or 2. Have to rely on the goodwill of the SaaS not to suddenly start raising their prices (the comparison here is passwords, which are free).
Before you say that switching providers is possible, that doesn't really matter. Let's say I stored the passkeys on my iPhone/iCloud. And then it got stolen.. whoops! Now I must at the very least acquire another Apple device until I can reach any of my accounts, i.e. I'm tech-dead until I do so.
If switching is not frictionless, it's an absurd level of lock-in, almost making it impossible. I have to go into every single account and add a new passkey? What if I forget one when I switch, then I'm out of luck and can never use the account again?
There are choices.