Mine neither...ambient display behavior is weird....doesn`t work quite well. Maybe is an L bug...
It does this to conserve battery.
Yeah but I've read that ambient display uses a lot more battery than the Moto Display because Ambient Display uses the Snapdragon Processor while Moto Display doesnt so Moto Display is more battery efficient lets say .... I havent tried it myself to be honest.
Moto Display knows when you reach for the phone because of the four infrared sensors in the corners. I heard that activating Ambient Display deactivates those sensors, so the phone doesn't know you're reaching for it.