tell me again why a hardware wallet would be immune to government hardware backdoors?

For example, because you are smart and made your hardware wallet from chips that made in another, preferrably rivaling jurisdiction. Since hardware wallet don't need networking to do the job, only USB, even if your PC is backdoored, they can't access hardware wallet internals, all what they will see is just an USB device that generates ready-to-send and absolutely public transaction block after you press a button on hardware wallet if you want to spend some coins. To receive coins you don't need to do anything with wallet at all. Also, chances that your local authorities could use rival implemented backdors is minimal even if your hardware wallet will fall to their hands.

However, I think it is not a very good idea to use hardware wallet. It could broke, seized or be lost. If you by design have no ability to extract private keys from it after wallet initialisation and save them on paper or somehow else, then you will be screwed.