That is an intended feature that let's you see any sub launched at one of your outposts.
I think it is mainly to make it easier to react to attacks, especially speed boosted ones, made from across the map, which are counterintuitive to the nature of this game.
“All warfare is based on deception. Hence, when we are able to attack, we must seem unable; when using our forces, we must appear inactive; when we are near, we must make the enemy believe we are far away.”
― Sun Tzu, The Art of War