Google was moving to vector rendering instead of static images for Google Maps, which uses a lot less data, so Apple wanted that. Google in turn wanted a lot more data from Apple about the user making the map requests. Apple didn't want to give Google more user data, and Google would't give Apple the better map product without it.

So Apple pushed ahead with their own maps instead, hoping that they'd be good enough to keep people from wanting Google Maps, which ... didn't pan out. Instead, Apple was forced to allow Google Maps in the app store, since their own maps weren't good enough, and people were complaining. So in the end, Google got the data, since lots of people use Google Maps instead of Apple's maps.