This is because Google is really pushing the image of being the "place AI is happening." They're doing the same amount of ML stuff they've always been, but it looks bigger because they're focused much of their marketing on it and attempting to associate their work in people's minds with the kind of "AI" that's just futurism for now.
I think the reason they're pushing so hard, actually, is that they're in a dogfight with IBM (i.e. Watson) over who enterprises will call if some VP gets the idea that they want to "solve problem X with AI."
The timeline is more they hired Hinton, got a bunch of neural network street cred as a result, and then hired a bunch of Hinton's acolytes, and then acquired Deepmind. From the outside, it seems Dean or some other higher up had the foresight / luck to bet big on neural architecture research just as the engineering started becoming practical.
I think the reason they're pushing so hard, actually, is that they're in a dogfight with IBM (i.e. Watson) over who enterprises will call if some VP gets the idea that they want to "solve problem X with AI."