The reason (afaik) is that you can enroll a developer key and re-lock the bootloader on a pixel, so your phone will check OTA updates against the enrolled key to be sure you didn't get a compromised update. This is not possible on other hardware, I guess.

I also want to be as far away from Google as I can, but I felt as though the hardware was probably a loss leader for goog and worth it to me for what I would gain.