> If you can get attestation without those restrictions, "sure, why not", and a Yubikey seems like a way to do that which could avoid those restrictions.

Remote attestation is never to your advantage. To do it at all, they have to restrict you to a specific set of device manufacturers and yours may not be on the list.

Then, what does it get you? Google-approved Android phones are allowed, but any attacker can trivially get one of those so knowing it's that type of device is completely worthless. All it does is prevent you from using some other type of device.

Notice that this is different from keeping the key in a HSM, which you can do without remote attestation and without the other side having to do anything at all.

Worse, the "approved" devices often have worse security than the one you want to use, e.g. using a Yubikey as your HSM will generally be better than using a phone which has orders of magnitude more attack surface and is constantly connected to the internet, but the phone is way more likely to be on the approved list than the Yubikey.