Probably Aus wanted to cancel the French project but push the announcement of the jobs consequences of the decision until after the next election by this 'review', which I suspect will conclude that SSN's are not realistically feasible for Oz at anything like an affordable cost. If they really want SSNs, the quickest, cheapest and easiest way would be to convert the Attack class to nuclear, i.e. make them Barracuda class but with US torpedoes and systems. This would also avoid NPT issues as would use LEU reactors.
As for the original procurement, Oz should have went with the Japanese offer and just bought them off the shelf.
Former PM Malcolm Turnbull, under whom the Attack-class program was signed, and who has been a vocal critic of Morrison's shift to nuclear boats, mostly in terms of the failures of diplomacy and subsequent rupture in relations with France, said a couple of weeks back that one of the reasons the French bid was selected is because it would have allowed for a smooth transition to nuclear-powered boats if that was subsequently deemed suitable.
Allegedly, the problem with a French nuclear boat is that French reactors use LEU and therefore requires refueling every few years. This would mean either regular lengthy dispatches of boats back to France for refueling, or alternatively creating the necessary infrastructure to accomplish such refuelings here, which was held to be a very expensive undertaking. The HEU reactors used by the US Virginia-class do not require refueling during their service life and are therefore believed to be more compatible with Australia's lack of nuclear infrastructure and expertise.
I don't have the expertise to evaluate those claims, but I say "allegedly" because it's clear that AUKUS is as much a political/strategic arrangement as it is an acquisition program -- arguably moreso. It's difficult to tease out the precise nature of how these factors are entangled with one another, but their entanglement certainly leaves open the possibility that the technical arguments re: the merits and requirements of LEU vs. HEU are simply being deployed to cover what was fundamentally a political decision, i.e. to formally become an American vassal state.