Another way of looking at this transition is that it was the inevitable result of the shift in relative prices implied by the depreciation of the exchange rate. But a third interpretation is that it was enabled by a psychological shift. In the era of ‘protection all round’, the presumption was that Australian industry couldn't compete with overseas suppliers.
That was why it ‘needed’ tariff protection. If you see yourself as inherently uncompetitive, why would you even try to export? But once Australia started opening its economy more to the rest of the world, exporting started to seem possible. And once you start believing you can compete, you have a chance of being right.