They'd be the only Subs on the planet with reverse-gear if they're anything like their tanks and other motorised vehicles designed to defend a country...
I don't know the full details of this deal gone bad but have seen enough bullet-points to think that like any other multi-billion dollar contract, there was a get-out clause that Australia excercised after long delays starting the project, price increases, and a realisation that these Subs would be obsolete before they got wet in an industry that evolves very quickly with technological advances. Plus they'd rather deal with long term allies like the US and Britain instead of ungrateful fucks who say Australia has done the wrong thing, while the bodies of some 50,000 Diggers who died fighting to liberate their country are buried under their feet. Fuck them, who gives a shit what the French think.