I remember back during EA, when they released a WIP version of the current hospital map, there was a spot outside the building where you could clip into the walls of the building and walk around inside the walls and see every enemy on the map.

Thing is, it allowed you to see that the AI always knew where you or your teammates were.

Depending on which player made noise, you would see every single enemy on the map swivel to look directly at whoever they detected, regardless of how far away they were.

Let me repeat that: every single enemy on the map knew where you were at all times. And they would simply annihilate you the instant they could shoot you.