The problem is that WW doesn't bring anything other than steady DPS. We have no burst, no cleave, no utility, and no raid-wide DPS increase like Shattering Throw, Skull Banner, or Stormlash Totem. We have no raid damage reduction, no passive raid healing, no passive self-healing, no passive damage reduction. Any marginal kind of utility comes at a cost to DPS (Chi Wave, the odd time that Zen Meditation actually does something, Chi Torpedo is impossible to take as DPS) which simply makes it not worth it to use. Windwalker is the prime example of a spec that does nothing but do damage.