The data as sent to Google (or any other analytics system) contains more than enough personally identifiable meta-data as to serve as a hugely useful database for the mining information on specific individuals.

Even just an IP address and device identifier is very useful metadata for assembling sweeping user profiles.

This creates a centralized data trove of hugely valuable data (why else do you think services collect it for free?) that is useful to both commercial and government interests.

This is why personal privacy matters, and why silently 'phoning home' without first getting explicit user permission is wrong.