Why hide em?
Because that's how they're best used to tactical advantage.
A "hidden" CV doesn't necessarily mean 6 sectors away from the action. It might be 5 miles off an unsuspecting base shelling the town, or it might be halfway across a wide stretch of water on its way to the enemy's rear.
OTOH, it might be hidden because the enemy has the port it goes with, you're not in a good position to retake that port just yet, and you have other CVs you can use to attack without risking one that the enemy will get back if they sink it. Why hand the enemy a valuable asset?
I don't understand why some people seem to think applying the most elementary principles of military strategy and tactics (keeping the enemy in the dark about your objectives and capabilities goes back as far as Sun Tzu, Homer, and the Book of Joshua) constitutes dweebery. It's a game and the object is to win, as long as you're not cheating or playing dishonorably.