There are so many factor affecting Holden's demise that one or two simple answers won't fix the problem.
The dollar is too strong and remains so beyond expectations that the fall of the mineral sector would see the dollar fall in value. It hasn't fallen yet to anything like what was anticipated.
Wage costs are too high, particularly compared to South East Asian and Korean wage rates. There is no way Australian industry can ever match the miserable wages paid in those countries, even though some here would like them to do so.
There are too many different makes and models for any local manufacturer to be able to sell sufficient numbers of vehicles to amortise their costs.
Tariffs are amongst the lowest in the world.
And finally, Holden is not building the sorts of cars that Australians want.
Typically, the **** fight has started in parliament, with the Opposition blaming the Government for allowing Holden to fold. That's laughable, when you consider that some of the factors I listed above are directly due to Labor policies. (lowered tariffs, support for union wage and conditions demands). The "level playing field" that is so beloved of politicians of both persuasions (but more particularly the Coalition) is a bad joke. We have made fools our ourselves believing that other countries would "play fair" and lower their tariffs or permit greater market diversification like we did.