That's a very broad statement to make. I'm sure you have a list of the dozens of such occurrences in the tens of thousands of Qantas flights "in the last 20 years".
3 on the ATSB website I've found, 2 actual landings where no statement was made that they were going to go below minima and did, the A330 at Sydney, which only indicated a PAN call so they could use YSCB as an alternate, not an intention to bust minima, and the Mildura incident. And Adelaide again in fog where they had prepared for an autoland after a missed approach and holding, but weather cleared to above minima during the approach. While I agree you might see this from other operators, they haven't pictured in the ATSB notes, so must be better at getting away with it.