To play devils advocate here, because I agree those old videos were stupid, I think the point was survival in the case of indirect hits. If a building is bombed

To play devils advocate here, because I agree those old videos were stupid, I think the point was survival in the case of indirect hits. If a building is bombed nearby and you're not close, hiding under whatever is similar to protecting yourself from an earthquake .. that is any debris that could fall from the shock.