It matters a great deal if people have to write out questions in advance, or during the talk, and a moderator then reads out the question. That mechanism improves question quality and cuts down on the first three motives cited. Yet it is rarely used. In part we wish to experience the contrast between the speaker and the erratic questioners and the resulting drama.
I like the second commenter’s suggestion: “Take multiple questions at once. The moderator will take say three questions from three audience members before giving the presenter a chance to answer them one-by-one.”