That's a great question. I cannot conclusively say that Google Play Services does that, but I cannot think of another reason for why Android would be set up that way.
Quite possibly for sensor fusion. E.g., combine with WiFi triangulation, accelerometer deltas from last fix, etc.
Play Services has a lot of stuff in it because it's easy for Google to upgrade it without going through phone vendors or carriers. It was a way to counteract the effects of many phones being on old versions of Android.
I welcome any alternative conclusions though.