It may be convenient to blame the French (isn't it always?) and indeed the deal was not going smoothly, but these are hugely political decisions and I think a key to what has happened is American pressure on Australia.

The French are not only 'pissed off' for commercial reasons. The deal was part of a long term strategy of France in the region, with India and Australia being the two main partners, so this has serious consequences for them beyond a simple arms sale.

Now, on the other hand, two good questions are whether the Australian ever discussed the possibility of France supplying nuclear-powered submarines instead of conventional ones, and whether France would have accepted. I don't know the answer to either though I'm doubtful about the latter and that may be an objective and very good reason for Australia to switch.