Totally agree. I was super excited for this feature too. I ideated this potential idea as a Facebook Portal killer long before Apple announced it.
Spoke to Apple TV Support - went to senior tier. That was the one of worst experiences I've ever had with Apple Support. By any chance have you recently changed the email for your Apple ID? I have and it seems to be a common theme.
See this thread:
To be 100% clear, I'm having all the same issues. My account, the default account on the AppleTV, does not show up in the user list in FaceTime and scanning the QR code just fails (Times out I guess) without error.