Australia simply didn't have the political levers to prevent it. They had bet on the wrong horse. Second, Asia's economic situation deteriorated and so did political stability. The most important country to Australia is Indonesia, which is near chaos. The instability was inevitable.
Political stability built on prosperity lasts only as long as the prosperity lasts.
Australians first underestimated the extent of Asia's economic problems and then refused to see the inevitable consequences. Suddenly, the sea lanes, guaranteed by regional stability, were no longer secure. No one can guarantee what that line will look like six months from now, let alone 10 years from now. The basic premise of stability evaporated. Australia did not expect this.