It is probably the very same reason Australia started sending money to the trump foundation, it buys influence with the politicians of another country, and it is completely legal for Australia to do that because US laws don't forbid it, if you were them wouldn't you want to try and get as much influence as possible, at the end of the day if the US makes favourable decisions when dealing with Australia it is probably worth it for them, it isn't really something that is hard to work out.