[maratc]

There is a ton of other information. E.g. for the “security” you are asked to provide a backup email address for your Google account. Also, for the same reason, everyone is now required to provide a cellphone number. If you used one of your Google accounts as a backup for another, or used the same recovery phone number for both, these two accounts can be linked to a same person. This comes in addition to other information about possible links, like geolocation or other trove of data they might have. If you added several accounts to check emails, your phone checks all of them every couple of minutes, from the same IP at the same time, whether you’re at home or not.

In short, the amount of data you are passing to Google, willingly or not, allows them to link these to a single person — you — with an extremely high certainty.