> That's no worse than before, where you could use the private key to undermine the encryption.
>
> You could also end up with a much better system if you encrypted the session keys so that only the auditing device can decrypt them.
We're speculating about the trust model and the constraints it must operate within. The private key isn't getting transmitted continuously over the network, so perhaps with some trust models transmitting session keys is equivalent, better, or worse.
Given that the people actually working in the space have clearly put a lot of thought into how to best fit their needs, I wouldn't presume that they got it wrong.