I think there's somewhat of a conflation of concerns. It sounds like your concern is, I have a credential manager and want to migrate to a new credential manager. I just want it to be simple to migrate my massive number of passwords, right? I need to bulk export + bulk import. EASY. But... what if your first password manager has a bug in the seed generator? Oops, you have to rotate 500 passwords now... there is no easy, off the shelf solution for that. It's basically the same for hardware-bound passkeys. If you generate hardware-bound passkeys, you're not going to simply replicate them to another hardware-bound passkey. The whole purpose of that type of credential, is to make it hardware-bound. There are a lot of meaningful reasons to do that from a security POV.

Now, I think what probably needs to be made clearer, is that if you do want that kind of credential, you shouldn't be using TPM-backed passkeys. You should be purchasing independent hardware (FIDO2 hardware keys) or only make software+transferable passkeys. Personally, I have several hardware keys and I register them with one being a backup. If the vendor posts a vulnerability notice that there's some big gap in their hardware, I will have to go and rotate every passkey. I know that is what I am signing up for, but maybe not a lot of people do.