In my experience, the Google Play Services play a big role in that. They get updated independent of the OS, which is in some ways a good thing, but does play a

In my experience, the Google Play Services play a big role in that. They get updated independent of the OS, which is in some ways a good thing, but does play a role in things gradually getting slower. My first phone for example became essentially unusable thanks to those, as my internal storage got completely filled up. And it's Google's main-highway for collecting user data. It obviously takes battery and processing power to tell Google everything about you.