The way you state this is as if Google is absolutely transparant about the data they're gathering and processing. Yet in practice it's nearly undoable for even experienced readers.i get emailed on a regular basis that Data processing agreement X of Google Service Y has been changed. Than there's is also the plethora of dark patterns within Google, for example the location functionality on Android. I get prompted that my location functionality is not working and that I must enable wifi tracking as well. Location is just working fine, be it on a worse resolution. Now if you'd be honest in the prompt, you wouldn't suggest the service is broken, but gave it less attention. If Google were really honest and transparant on all the data they're using, and making it easy for users to make a choice in how and what, than my take is that most users would opt-out.

But luckily google provides us with a completely gdpr compliant opt-out for Google Analytics.