Krishnamurti spoke of choiceless awareness because our awareness is selective. We don’t know what it is to be choicelessly aware because our conditioning alters our awareness. We are less aware of what actually is than of what should/should not be. That is, the mind is conditioned to be dualistic; divided by the conflict between what actually (choicelessly) is, and how our conditioning alters awareness to conform to the dualistic reality of our experience.
The conditioned mind cannot imagine what choiceless awareness is. It can grasp the concept but it can’t be choicelessly aware without losing its identity, the result of its conditioning. To be selectively aware continuously the conditioned mind must never see its selectivity. For it to do so is to awaken to the dream/nightmare its experience has crafted.