This might come off as projection, but in my experience, HN has a lot of people who pride themselves on their rationality, and part of this is giving off the image of never joking and always being serious. You can see this when people get mass downvoted for making jokes, which is also uncommon in other programming communities. Somehow this often spills over into metaphors as well as jokes. I think that jokes and metaphors are quite similar in that regard, both not to be taken totally seriously and/or literally. The HN insistence of being above jokes inevitably leads to being above metaphors.