Google’s primary goal is not to sell hardware and generate revenue from mobile advertising, but to gather signals for better targeting advertising, and to provide more useful information to the user so it becomes a must use service:
An Android device, properly signed into a Google account and running all the Google Apps, generates an endless stream of little bits of ‘signalling’ information, way beyond what Google gets from a desktop search user even if they’re using Chrome. It knows where you live and work, how you commute – and which phone numbers on web ads you dial. Unlike a web browser, you are probably always signed in to Google, so all of your interactions with Search, Maps and anything else can be linked together. (This, of course, is also the main purpose of Google Plus.) source
Just like Google Analytics