Outdoors bodies decay this allows you to loot corpses that might be dead on top of each other. However in mission areas these same bodies do not decay. The issue is that in previously designed missions dead bodies were placed in the mission areas so that player's, as part of mission objectives, could interact with them. If bodies decayed then these objective oriented missions would become very broken so dead bodies in mission areas don't decay.
Now we have the PB missions with lots of mobs in each misison area. So now we have to live for the time being with the legacy of the early design. Not a perfect world.... /sigh.
