Moon drawn on this card is not the same as the moon controlled by Princess Luna. Group of impious ponies, now nearly gone from entire Equestira, call it an Ancient Moon. According to them, Princess Luna has sealed this Ancient Moon, which moved endlessly itself and changed its appearance, in a place where nopony could ever find and created a new moon to take its place.
Perhaps that is the reason? Different from moon of Princess Luna, Ancient Moon card represents cycle of Timber wolf-like insecurity, unpredictability, stealth and revealing. Nights with presence of this Ancient Moon must have been really dangerous compared to present time.