Why does written communication require more organization than oral communication?

Oral communication can clarify and explain ideas in response to an audience's questions and comments, whereas written communication cannot

Written communication typically requires a thesis statement, $3$ supporting points, and a conclusion

Eye contact, facial expressions, and body language are more effective communication methods than words, so additional explanation is unnecessary

Speakers tend to be more organized than writers, so writers need to think through and structure their points more carefully