Southern Sun Frequent Guest Pricing

Southern Sun Frequent Guest Programme. I've been a Southern Sun frequent guest member for a number of years and recently picked up that Booking.com was offering rates which are more competitive than Southern Sun's Sunbreaks promotion. I had contacted Southern Sun to notify the difference in rates and queried if Southern Sun would match the rates at minimum? The response from Southern Sun was really poor where they state that their policy does not allow price matching and there is nothing that they can do in this case?

My question is, why would you be loyal to a brand where third-party sites offer better value? Why wouldn't Southern Sun have a strategy of ensuring loyalty from frequent guests? I have had a similar occurrence in the past where the hotel chain was happy to address and ensure that they retain your business.