The pipes tend to be insulated, the temperatures don’t really get very low (coldest I’ve ever seen is -10° and that was for a couple of hours), and that’s at night, and the cold “season” is very short. It takes time to freeze pipes, and here it just doesn’t get cold enough to do that.
I don’t know these games (I’m out of the loop on commercial and board games for the past 20-odd years, sadly) but I have loved this mechanism since playing the earliest rummy-family games from China. (Majiang is the most recent of a loooooooooooooooooong line of build-and-discard games in China.) The added spice of worrying if someone is going to use your discard to improve their hand or even complete it before you can do yours is part of why I like playing the rummy family.