Google's business model is shaped to scale gradually – by you paying with your data.
In the old world, you would buy services from a provider in a packaged way. The more service in the package, the more you pay. You pay money, you get better service.
Google exchanges "money" with "data", since you pay with your data for every service. The more data you give to Google (by using it), the better the algorithms become, the better Google can serve you.
Or in other words: The more data you give to Google, the better Google can sell you as a product, and the more it earns for developing the algorithms which in exchange serve you.
(cc-by-sa) since 2005 by Konstantin Weiss.