Why Google play services not included in Doze mode

I'm using Nexus 5 and 6P, Android 6 having a feature called "Battery optimization mode" or Doze mode (in short). It is allowing apps not to run, if they aren't used to avoid battery consumption. Google play services consumes more battery, RAM and CPU. But it is not included in Doze mode. I've sent multiple feedback from my devices about this issue, but Google is not hearing at all. Anyone please help me clarify, Why Google play services not included in Doze mode?