Why did we buy 8 subs for $368 Billion $46 Billion each ?

Why did we buy 8 subs for $368 Billion $46 Billion each.

Would it have served Australia better if we would have ordered the "Gerald R. Ford-class" the Most Advanced Aircraft Carrier in the World.

They are supposed to cost around AUD $20 Billion each.

So 8 of them would be AUD $160 Billion.

They would be more use, and impressive than the subs.

Could have saved a few hundred Billion too ?

Any thoughts ?