The main reason for the subs and indeed, the increase in Australian defence spending and mobilisation is the threat of China taking Taiwan.
The reason we got second hand ones was America can't make them fast enough. $5 billion dollars each I believe. America needs to make 2 a year but can't keep up. Probably cos China has a stranglehold on critical minerals for the development of defence assets, along with a hollowing out of manufacturing like most western countries.
Australia, like the rest of the developed world, will enter a technological dark age if China takes Taiwan.