We couldn't rely on the exchange rate as an anchor, because we didn't have the sort of domestic structural flexibility consistent with a pegged currency, particularly given the nature and size of the external shocks which hit the Australian economy. And a policy of completely unconstrained discretion lacked credibility precisely because there had been two decades of high inflation.
So when inflation came down during the aftermath of the recession in the early 1990s, to rates which were lower than anything seen since the 1960s, the question was how to take advantage of the opportunity to lock in low inflation as economic growth recovered.