Why wouldn't the water cycle constantly adds pollution to the air be important in the water cycle

This wouldn't be important because the water cycle is simply a series of events that occur starting from Evaporation, condensation, sublimation, precipitation, transpiration, run off, and lastly infiltration. Though you may think that through a certain step the water is adding pollution to the air, this is not something that is being examined or asked of you to identify when specifically dealing with the water cycle alone. Hope that answers your question.