Is it a mental thing? Do we not have the ability to see a gold jersey and realise we have to do every thing we can to ensure we win?
I know that I'm going to get blasted for this but here goes anyway:
I reckon it's your national failure to evolve with the game over the last nine years.
Say what you like about Clive Woodward (and you could say a lot) but that guy schooled New Zealand and Australia in 2003 in Wellington, Melbourne and of course the final in Sydney. And the lesson was: Stephen Jones and all the other NH commentators who were saying that Super Rugby/3N rugby was powder-puff basketball rugby were right. NZ and Aus could no longer rely upon superior athleticism in slick attacking interplay to subdue other countries.
NZ took the lesson onboard and focused on providing a solid platform, particularly from set piece, particularly the scrum.
In contrast, Australia didn't and continued to rely upon gamesmanship from Gregan and co. to con referees into obtaining near-parity (then) and importing personnel from other Unions to make up for the inherent deficiencies (now.)
You'll hear from time to time people describe the 2000 Bledisloe in Sydney as "the greatest game ever." 74 points were scored in that encounter and it wasn't, it was a game of glorified 7s. My opinion is that your lot have largely failed to move on and are pretty much playing the same game.