The credit card business in Hong Kong is incredibly competitive. There's no need to pay an annual subscription - most cards offer one or more years free, and then you just have to threaten to cancel to get them to waive the annual fee.
Apart from the introductory gifts there are a variety of special offers, some of which seem to make no sense at all. For example, DBS is offering a $20 coupon for every $60 you spend at Pizza Hut. The coupon is only valid for about two weeks, but when you use it there is no minimum spending requirement.
However, the part I find truly puzzling is that they are going to so much trouble to encourage customers to use their credit cards when they have a pizza delivered, when I'd have thought that would be the very last thing they would want. Surely they want the drivers to take cash and get back for the next delivery, not spend time taking an imprint of the customer's credit card.
On top of that, DBS give you 90 days credit on your $80 pizza.
Desperate or what?