The "forgot password" flow involves accessing your email. And accessing your email without having access to your passkey requires a device that has previously logged in to your email. And the device that has previously logged in to your email is the same device where your passkeys are stored, which is to say, the same device that is now lost or bricked, which is the reason your passkeys are lost in the first place.
And sure, you and I have multiple devices. We're in the minority. Most people just have the one. Without another way in, they're irrevocably fucked.
We fixed this on mobile years ago but email is still a goddamn mess. Moral of the story: never get locked in.