Here's a thought on this issue, and I have absolutely NO inside knowledge on this, but what if in pure marketing/revenue terms, you are seen as a almost certainty.. as in long term loyalty, unlikely to shift, so revenue is assured (from QF's point of view0 thus the effort/spend they need to make to keep you is less than someone new they're trying to get. I'm not a marketing person but I understand a cor concept with loyalty is that winning new customers is X times more expensive than retaining loyal ones.
The interesting thing is if you (or indeed I, as it looks like may happen with me, not for deliberate reasons but the way things may work out) show a lower booking (forward or used) level, or stop for a bit (possibly moving to another carrier) then they may pop up and take note and throw something out there "hey, remember us?" kind of thing. Or not.
It may also be that whatever metrics used to "value" a customer's worth to the company just don't reach certain thresholds. note *I* am not trying to say someone just doesn't matter that much ("he's just not that into you!") but in this kind of world when QF's objective is to capture, maintain and hopefully raise ("It's about me, not you") then it may be seen a regular spender that has a known pattern is perhaps not as high on the radar.
I'd also suspect where there are pax that represent >5000 SC's, or 7000 or whatever in a year.. that's serious revenue. Serious spend. Scary. I'd love to know the top SC earners at QF - or rather how much, not who... I bet the mind would be boggled.
It could also come down to matching routes flown, partners, matched to competition (eg: if you're flying to LAX mostly and the competition is UA and VA that's not like you have the choice to throw serious revenue at a SQ to fly to europe on).
All I know is that in big businesses like this that invest heavily in loyalty and revenue like this, it's not as simple as reaching a certain set goal no matter what is published - I'm sure of it. Mix of fares purchased (paid F? paid Biz? mostly sale vs. flex fares?) etc can all come into the mix.
Me.. I think I made P1 with 3700ish one year and 3950 another. Sure, over the line but not by much. I'm not the droid they REALLY are looking for with the paid full-J and F fares (IMHO). I mostly buy I's and D's or fly on OW partners (before the devalue) and stuff like that, plus domestic trips. I am sure they model all this stuff internally and assign each customer a certain "value" score based on this kind of data.. and then make decisions based on that.
again, I have no real idea what QF does.. just some random thoughts.
and hey I'm cool.. win or no wine, books or no... the fact that I've been well looked after in the air, which is what I pay QF for, my J->F upgrades have ALL gone through when most wanted and so on.. that's why i value the status. Extras are just that.. nice (and unusual) unexpected surprises. I'm not hanging out for an invite to Boxing Day test or a jumpseat on the 763 or something.