Why would Doze feature need motion detection? I do not see any reason mentioned by Google for Doze mode to get activated only when the device is stationary.
Is there any specific advantage for doing this only when the device is stationary? What is the need to even waste resources checking for motion detector readings, when this can simply be achieved whenever the screen is off.

I am asking this because my phone is in my pocket for most of the time and because of that Doze mode will not get activated. I think there are many more people like me, so I don't understand why google chose these specific constraints for Doze mode.
It is based off of the assumption that the device is not being used at that time, so it will enter Doze Mode.  How do you know that Doze is not being activated?  Clearly while in your pocket, if you are walking/running or moving around, the device will detect motion and not enter Doze Mode.  That's how they chose to have it operate.

Here's an explanation of it taken from here.


  Doze mode is different in that the entire device is taking a nap, not just the least-recently used apps (such is the case with App Standby). Doze mode is activated when the device is not plugged in, when the screen is locked, and when no motion has been detected for some time. These assumptions imply that the user has put down the device and walked away. So, when they come back and pick their phone up off the counter, it should not have dropped to 30% battery. It should, essentially, be in the exact state it was in when they placed it on the counter. Right?