Frankly, because Australia has things that the USA does not have and really needs. Australia is a stable and reliable political friend in a region of the globe that is close enough to the antipode of mainland USA. Our proximity and unused land affords our US allies with space and privacy to operate with relative comfort. Their bases in Australia also have much shorter logistic chains to operate compared with other remote locales like islands as well.

The USA would be impacted militarily if they lost Australia as an ally. Not irrevocably, they’d get by. But it would cost them a lot more than the simple civility and respect it takes to maintain their relationship with Australia.

Neither nations really needs the other. Our partnership has been convenient for both of us, and it really would be a shame for both nations if that partnership were to lapse.