Why don't we know we are dreaming while we are dreaming

The reason we dream is that the manas constantly grasps and clings to certain dharmas, and the eighth consciousness, in accordance with this, gives rise to the dream. Dreams belong to the Image-Only Object, discerned solely by the mind consciousness without the cooperation of the five sense consciousnesses. Because the conditions for the arising of the Image-Only Object are relatively few, as long as the manas clings to and dwells upon certain dharmas, the Image-Only Object can appear; then, when the manas contacts the Image-Only Object, the eighth consciousness gives rise to the mind consciousness, which discerns the Image-Only Object. However, in dreams, the mind consciousness's to unwholesome conditions, and can lead the six consciousnesses to do good and create wholesome karma. In this way, a wholesome mind will correspond with wholesome destinies, and the likelihood of rebirth in a wholesome destiny will be relatively great. Moreover, since the mind consciousness also knows how to choose a wholesome destiny, there is a possibility of being reborn in a wholesome realm.