The idea is that the Supremacy’s hyperspace tracking device acts as a static hyperdrive itself when active. It’s static in that the Supremacy enters hyperspace with this device but doesn’t move, allowing it to use its sensors to find other ships in hyperspace.
I’m thinking of it like a periscope on a submarine - part of the sub must leave the water for it to work. To continue the analogy - if a speedboat were to hit the periscope, it would damage the sub, whereas if there were no periscope the boat would pass overhead with little disturbance.