Last thing you want is to be caught in hostile territory without your armor on!

Greek hoplite armies of the period generally carried most of their supplies via pack animals and porters. As such armies were made of middle-class militiamen who provided their own equipment, anything a soldier would not have thought to bring along and not been required to was very likely to be missing, and there are numerous accounts of soldiers in this period dying of exposure because they did not bring the appropriate apparel to their destination - or to the detour they were forced to take!