[londons_explore]

Perhaps because some testing needs to be done on physical devices in a real lab?

"Please test this build of Chrome on these 1000 various models of android phones" sounds kinda hard to automate.

Even if you had automated it, you'd probably still need someone in the office to poke hardware that locked up, etc.

[Symbiote]

I don't know what Google use, but a friend worked on a system some years ago that used a robotic "finger" to press on a phone touchscreen, for testing. This was for a mobile phone company (pre-Android/iPhone) to check their OS worked.

I wouldn't be surprised if even the best of those systems requires some human supervision.

[kube-system]

They already have that problem solved:

https://firebase.google.com/docs/test-lab/

As do many others:

https://aws.amazon.com/device-farm/

https://appcenter.ms/

https://kobiton.com/

https://www.perfecto.io/

https://saucelabs.com/solutions/live-testing