If you wanted to get nitpicky, I guess that you could argue that the Triple Triad is so prevalent in their society that people make cards (or have them made) of their friends and family members. That would explain why they are rare and are most often carried by parents or close friends. It's really not THAT much wierder than people who put their kid's picture on T-Shirts and coffee mugs and jigsaw puzzles, I suppose.