People seem to be overlooking the fact that a set of SAPI plates in a plate carrier are VERY heavy. Roughly 30 pounds or so. Realistically speaking, anyone who is stuck moving on foot in a survival situation would never justify carrying that much weight which could instead be used for food, water, ammunition etc. Now, if you were late in the game, had vehicles and a support group to assist you, it becomes a possibility. The weight penalty would be negated somewhat. Soft body armour is a whole other story, but it should be limited to stopping pistol rounds only.