Because more than likely Australia along with the rest of the UK and EU have been hijacked by a foreign entity. The citizens of these nations have all been betrayed by their governments.
Things must play out exactly as they currently are to ensure Australia acquires its future time powers. Changing the past would likely make it so that Australia doesn’t eventually come to control the time power in the future but some other country does instead, and thus the past could never have been changed by Australia to prevent bad things from happening, which would again put Australia in control of the time power since the past was never altered. The only possible future is one in which Australia doesn’t fix the past, and all other possibilities self-correct back to this alpha-timeline.