There is no win here for Google! Less users (not everyone is going to install it), less data coming in, more money spent, having to hire more dedicated iOS coders inhouse at Google...
People have a weird definition of "win".
Now they have a mapping application, which means now they have users.
I still have a standalone GPS in the car which we will definitely not need once we all upgrade to phones with turn-by-turn directions. I have relatives that pride themselves in not needing smartphones, but seeing turn-by-turn was very compelling.
My question which I haven't seen a definitive answer on is if Google had the ability pre-iOS 6 to do turn-by-turn? They already had it on Android. Were they slow on iOS, or were key APIs missing?
The original Maps app was written by Apple and consumed data licensed from (and presumably hosted by?) Google. Apple wanted turn-by-turn on iOS, but the data required was not part of their original deal with Google. Google was willing to license it, provided that Apple give Google additional data: presumably anonymized data about where users were for Google to use to provide better AI. Although it's quite possible Google wanted better hooks to serve ads as well. They couldn't reach a deal, so Apple went their own way.
Apple and Google were certainly technically capable of building Google-backed turn-by-turn into iOS 6, if not much earlier.