The issue, apparently, is that some of the components are about to cease being manufactured.
By ordering now, the Australian government can have them manufactured as part of the last US production run.
If the Australian government delays, it will have to eventually pay for the whole production line being started up again.
Yes, I saw that and started to mention it as a justification. There are certain defense related industries that we keep alive even at a loss sometimes; shipbuilding, aircraft manufacture, certain electronics, steel making, etc.