Because while both countries use the "dollar," it is not the same currency and cannot be compared directly.

Australians also tend to make more, and thus have a higher cost of living. If an Australian is making less than the equivalent American, someone or something failed somewhere and that person is not going to have a good time. If an American is making more than the equivalent Australian, that person is probably enjoying life.

It's why pushes for minimum wage are so poorly thought out. Okay, you double everyone's wage, it means the companies that pay them pay twice as much, so they will raise costs to compensate. They're not going to take a pay cut. With everything going up, those who get paid more have roughly the same spending power (so nothing has really changed for them) but those who didn't get paid more have it worse — and that's the point.