Though Korriban has only been reclaimed as home of the Sith Order in recent decades, its rich ties to the Empire reach back thousands of years. For Republic forces to set foot on the planet, let alone capture the Sith Academy and Dark Council Chambers, is a great indignity to the Empire's leadership.
It has been reported that, upon hearing the news, Darth Marr ordered the full destruction of the nearest Republic-friendly space station. While this claim remains unsubstantiated, it does correctly illustrate the enduring rage felt by many across the galaxy. Even if the Sith Academy is wrested from Republic control, it may never again be regarded with the same pride it once was.