So why do Google Play Services, etc. have full privileged access to a phone, including private data and phone call audio, but the user doesn't?

It is tech feudalism - you don't own anything anymore, you just get to live on the digital land of a bunch of ~trillion dollar companies.

At least, that is the goal.

IMO either everyone gets access at the user's discretion or Google has to sandbox their own GMS services as well.