The problem isn’t that the Aussies are retiring the F111’s; they are over 30 years old and that’s a long time to keep the plane working. As the article notes, the Aussies got more than their moneys worth out of them.
The problem is that we aren’t making a reasonable medium range aircraft to replace it. All the US Air Force seems to care about is high-performance fighters and long-range stealth bombers. Aarvaarks are considered “unglamorous” duty and the fighter jocks who fly and the ex-fighter jocks who set procurement policy don’t want anything to do with it.
The last of the medium-bombers. Peacetime militaries tend to purchase equipment without regard to wartime utility. “Cost-effectiveness” calculations frequently ignore factors relating to wartime utility.
Early in Afghanistan the USN was running F-14 “Bombcats” north to fly topcover for the SpecOps and Northern Alliance militiament. The F-14 had great legs and a respectable bomb load. Try doing that with the F/A-18. You don’t get near the coverage and you don’t have as many weapons on station.