My colleague once told me that the reason telecom providers took so long with Android software updates was because they had to verify that the phone meets regulatory requirements after the update. One of these requirements was being able to dial 112 (Europe's 911) very thoroughly. There was a legally prescribed process (by BNetzA, IIRC) for doing that in Germany. After a quick Google search, it seems like there is something like that mandated by the FCC in the US.

I wonder how the Pixel 4 passed it. Not just in the US, but in many countries.