Xtra Savings Card Declined

Since when does Shoprite cashiers decline the Xtra Savings when given to them? My mom bought Ritebrand butter yesterday and it was R20 for each of them if she swiped and R23 (R6 is a lot of money) if she doesn’t swipe. She gave the cashier the card but the cashier said no it’s okay there’s no need for the card. Why?