I can't even get a response from Google's support about the issue. (Although, based on what I've seen from other people in the same situation, the response would be pretty useless if I did get one.)
I'm still using the phone, because the hardware is perfectly fine for my needs, but it's slowly turning into e-waste as the software gets more and more out of date. (I replaced the battery about a month before learning about the bootloader, so it's good for another 3-4 years.)
Edit: I'm not the only one this happened to - see https://support.google.com/pixelphone/thread/14920605/google... and https://issuetracker.google.com/issues/73217322 and https://issuetracker.google.com/issues/68897739 and https://forum.xda-developers.com/t/rma-phone-from-google-is-... and https://forum.xda-developers.com/t/oem-unlocking-grayed-out-... and https://www.reddit.com/r/Android/comments/9xcdle/psa_rma_ref...