I’m describing using telemetry correlating which IP addresses/devices have used specific gmail accounts, nothing to do with the contents of those emails.
The gmail account just as a correlation ID has a ton of value in search.
The data from Gmail isn't what's valuable to Google, it's the fact that targeted ads are more profitable and Google can target you with ads accurately because you logged in and identified yourself to access Gmail.
The gmail account just as a correlation ID has a ton of value in search.