Presumably because fi runs on tmo. I'm on tmo and haven't been able to figure out the 5g issues. In my city the 5g is spotty and crappy and I need to be on lte to do anything consistently. When I travel to other cities 5g seems to work just fine.
I'm just hoping version 14 fixes the Pixel overheating issue whenever the camera is used for an extended period of time. Long distance video calls with family have been cut short several times for me now. :(