Agree - I have been looking for months for any award seat PER-SIN in March next year with no luck, until last week when a J seat popped up for several days around the time I wanted.
A few thoughts...
What if Qantas did release more award seats, and the demand for those seats is so high that they're snapped up quickly and therefore most folks never notice any additional inventory showing online?
Also, have you noticed some carriers (ie: MH...CX...JL...) don't show direct flights on the QF award booking engine? For example, search MEL-KUL and there will be a MEL-SYD-KUL option. But search SYD-KUL, and the direct MH flight option doesn't appear, and instead, shows a SYD-MEL-KUL, which didn't show in your previous search ex-MEL.
What if the Qantas Classic Award Search Engine does NOT show all flights, and that it looks and feels more like an ad agency than a flight redemption business. Pay more...give Qantas a better deal... get more online inventory listed.... get higher in the search results.
In fact, it may be showing flights that Qantas wants you to book instead of what is actually available. Because of the way award inventory works between airlines - Qantas could show you flights it makes a profit from, and not show other flights it doesn't make much from. Qantas may not want you to book award flights that it doesn't make much income from - ie: the realised revenue from points on non-Qantas group airlines may be less valuable than if the member were to NOT redeem those points at all.
Which brings me to the most logical question: how much do airlines pay/bid (directly or indirectly) to receive preferred listings in the QF award search engine? Why does Qantas not have to disclose preferential listings in their award search engine? Should there be a notice that certain flights are boosted/deboosted in the search results?
IMO any reasonable person who spends time analysing the classic award search results will come to a similar conclusion.