When most sites refer to passkeys, they’re typically talking about the software-backed kind that are stored in password managers or browsers. There are still device-bound passkeys though. Also since they’re just FIDO/WebAuthn credentials under the hood, you can still use hardware-backed systems to store them if you really want.

While you’re right that device bound and non-exportable would be best from a security standpoint, there needs to be sufficient adoption of the tech by sites for it to be usable at all and sufficient adoption requires users to have options that have less friction/cost associated with them, like browser and password-manager based ones.

Looking at it through the lens of replacing passwords instead of building the absolutely highest-security system helps explain why they’re not limited to device-bound anymore.

Sadly I’ve run into the same type of problem with a newer TLD as well. My solution was to get a domain in the older TLD space (e.g. .com, .net, .org). I doubt this will be the last site you run into that doesn’t support a newer TLD and the low likelihood that you’re going to be able to convince someone to fix the issue at every one of those outdated sites means that you’ll eventually need a backup domain for something.