The reason for the card is so that people that are non-SPG can participate in the program increasing the overall use of the program and decreasing the use of housekeeping. Which for the hotel lowers the amount of people they need to clean rooms, as well as the cost to clean sheets and what not. I'm guessing that is why they use the cards. There should be an option if an SPG guest just wants the points to make it so no cards are needed. The downside is if your points go missing... I guess you would know if the code wasn't punched in for your preference if you received housekeeping.