Because they know where I live, and therefore know that I have access to Aldi, Coles, IGA, Supabarn and Costco (spoiled for choice!). I usually shop at Woolworths because it is the most convenient and because of the QFF points I can make.
But I can easily buy my regular products elsewhere, and for the last 8 weeks I have been doing that. My Woolworths spend is now around 15% of what it was before - yes you read that right, I am buying 85% of my groceries elsewhere at the moment. And as they can personalise a points offer when they choose to, I would think they might care that a person who usually spends $400-500 per week in their local store is now (for 6 weeks or so) spending just $35-$50 per week. I now only go there to buy emergency items like milk or tomatoes that I ran out of. The other grocers are getting all my cash, and Woolies has the power to know that, if they cared, and lure me back with offers that might be attractive to me.