Why is Australia so good at sports?

Westi nailed it. The government puts lots of money into elite sports for coaching, all the way down to local sports for facilities.

Ths funding goes up and down. After the Montreal Olympics where Australia scored no golds, there was much spending, as also in the several years before the Sydney Olympics.

Unlike in the USA, sport doesn't play a big part at university but scholarships are made to several sports institutes where much elite training happens.