Because there is a difference in cover and concealment. When being shot at it is not smart to hide behind a building next to a gas barrel or a carboard box that the player can shoot through.
So the question comes in do I dig deep into the AI system to determine that, or let the level designer simply tag the safe cover locations. That is how I am used to doing years ago and was common in the engines I used.
I suspect the EQS system was developed to replace the older method I am used to, so will probably go ahead and prototype out a max test and see what happens.
Maybe using the EQS system, and simply tagging assets that are not to be used as cover would be a better approach.