It might also have a lot to do with the number of people who traveled first class to Australia, as opposed to the number of people who traveled first class between NYC and the European ports.
The French, and Dutch colonial ships had interiors that, in terms of over-the-top, made the garish North Atlantic ships seem tame by comparison. The Italian, Spanish and French ships on the South Atlantic runs had interiors that made the White Star, German and Cunard north Atlantic ships look like second rate boarding houses but, of course, were aimed at a different class of passenger.
And, by 1912, the White Star, and German, interiors in particular did not represent sophistication. And hadn't for about ten years. Ostentation, aimed at the nouveaux riches, is about as far from sophisticated as one can get.
My guess is that it was a matter of money, and perhaps a slight amount of elitism, regarding Australia, than it was the subjective matter of sophistication. Had there been money to be made in installing expansive first class quarters on the Australian run, it probably would have happened.