Because you don't have to outrun the bear, you only have to outrun the other guy trying to outrun the bear.
The market, both domestically and internationally, for good or ill, is moving towards a model with far less members attaining tiered status. Qantas have a (relatively) captive market and (relatively) little opportunity to scale membership internationally. It doesn't need to outperform the market on offering, so it won't.
I don't think they want them empty. But they do want them less at capacity and cheaper to run. And lounge access to be a profit centre, not a cost centre. Or is that the quiet part out loud?
Betting against the market then?