I'm not sure it is a great strategy. And I'm even less sure that it makes it a great loyalty program.
1/ It does mean that WW doesn't have any obligation for petty purchases which effectively reduces its obligation.
Given X % of all transactions are less than $30, this means that its financial obligation to QF is reduced by X (well X x $0.01 or whatever its points purchase fee is).
It's a great financial strategy- not necessarily a good loyalty strategy.
2/ Arguably the smartest people try to consolidate their shopping into one or two large ships, rather than separate little purchases in order to minimize the effect of the $30 threshold.
The smartest people are here on AFF etc.
Most people outside of AFF can't be a$$ed and will shop whenever convenient - this includes all the employed people shopping everyday during work hours for their can of Coke, their coffee, their lunch, their Chobani yoghurt and organic soy fair trade prepaid topups etc.
3/ Even for many savvy AFF-type frequent flyers, with the existence of the $30 threshold- I'm not going to buy $31 worth of candy bars, when all I want is one single Mars bar.
So I do two things - firstly, shop at the most convenient store - which is probably not Woolworths, and secondly, even if I do - I don't bother scanning my card, which means WW don't get the data on me.
Again - the $30 threshold is a smart financial strategy, it's not a smart loyalty strategy.
The behavioral assumptions in the model are flawed.
Ultimately you want :
1/ People to swipe for EVERY transaction - which means giving them something. Ideally points, but also the "discount with card" practice works brilliantly. WW have only been dipping their toe on this strategy- but Ralphs do it brilliantly.
2/ By giving them points on ALL transactions - it's the golden handcuffs. Yes the QFF bill is a large line item on the P&L but imagine the cost of marketing as a line item if you didn't have QF doing it for you.
You want data and handcuffs- things for which the $30 threshold does neither.