Tonight, I was going to post a new thread in the Wuxia Forum about why characters in wuxia novels are never seen playing mahjong despite the fact that it's a very popular Chinese gambling and recreational game.
I did a little research, and it turns out that mahjong is a much more recent invention than I thought it was. Mahjong's history dates back only to around 1850 (long, long after any Jin Yong or Gu Long wuxia novel was set), which is pretty "recent" in the context of Chinese history. Despite its widespread popularity today, mahjong was invented a mere 160 or so years ago.