It's not as though Google didn't have an iOS apps team or iOS apps prior to iOS 6. It had to develops apps such as Gmail, Google Voice, and more. However, the recent ouster of those other two apps increased the impetus behind Google's iOS development.
In the YouTube ad embedded below, Google tells developers they can "Do cool things that matter." The ad mentions such Google projects as Search, Gmail, YouTube and Chrome. Absent from the list is Maps, possibly because Google was caught by surprise by Apple's decision to kick Google Maps from iOS 6 (which we know was the case).
The ad links to a website with a full description of what the Google iOS mobile apps team has to offer applicants. It says:
It’s fun. People have misconception that we just copy and paste existing Google products to the iOS platform. But we have a lot of freedom and try to innovate beyond anything that Google’s done so far. We are always working on ideas to push the envelope on mobile search, and we collaborate closely with Google Web Search engineers to implement new features.Although Apple owns the iOS platform, it's known that Google wants to own the iOS apps experience on the platform. It makes sense: Although Android is the global leader in smartphones, iOS has a large market share, and every additional eye on Google apps helps Google's overall ecosystem.
Interestingly enough, as with many other developers, Google's apps don't necessarily align from Android to iOS. In fact, Google's Maps app on iOS has been said to be superior to its more mature Android app, something that Google hasn't tried to dispute.