The Hammerhead is intended to hold a position with full 360 turret coverage on all angles, rather than be able to point them all in one direction. There are systems in place to prevent the turrets from hitting the ship so whilst they can fire all forwards, it isn't an optimal solution. Recall that one of the Hammerhead's chief duties is protecting other ships from attack by fighters and small bombers; the Hammerhead is not a dogfighter, it's too large and too heavily armed for that. It's designed to provide, not firepower in one direction, but flexible, massed firepower in any direction while adapting to the flow of combat threats around the ships it's escorting. And when it's not escorting anything, the Hammerhead is designed not to be safe to approach from almost any angle.