The smart shopper might only buy in bulk once every three weeks when his favourite brand at a lower price, or twitch to the cheapest brand every week. A hurried or lazy shopper might always pick their favourite brand every week. If they buy one item a week the lazy shopper would have spent $5, while the smart shopper has only spent $3.
They've made 60c off the smart shopper and $2.60 off the lazy shopper. By segmenting out the lazy shoppers they've made $2. The whole idea of rotating the prices is nothing to do with the cost of goods sold it's all about making shopping a pain in the ass for busy people and catching them out.
