Since Google’s business is advertising, shifting industries away from paying business models is in their interest. If people are willing to pay for email, mapping and documents, Google’s business model is limited. Thus, using the outsized revenues they make from advertising on search, Google gives away Gmail, Maps, Docs, navigation, translation, et cetera, so no one can compete in those areas—to make free the norm for these services. If Google is giving away a quite good service, it’s hard to compete with them in that area, and so the economics of that business shift away from paid services to advertising-supported. And if a business becomes dependent on advertising for revenue, that’s good for Google, because they’re better at it than everyone else.
— Kyle Baxter