Wired: The Privacy Battle to Save Google From Itself by Lily Hay Newman:
Google is not a consumer software company, or even a search company. It’s an ad company. It collects exhaustive data about its users in the service of brokering ad sales around the web. To do so, Google requires an extensive understanding of the backgrounds, browsing habits, preferences, purchases, and lives of as many web users as possible, gleaned through massive data aggregation and analysis.