When thinking about MNK, this is something that eventually comes across my mind. And I think I can only describe how SE treats it as two things:
1. They're too married to how monk is now and are too stubborn to change it.
2. They genuinely don't know what to do with the job for whatever reason, despite having years of feedback to work off of and quite literally endless amounts of inspiration to design a fist fighting job, especially from their own games.
I lied, there's a third reason being that they don't care. But I really don't want to believe that.