There are so many ways that writing can miscommunicate. It's a very low bandwidth, high latency medium. The state of mind of the reader can often color the message the author is trying to send in ways the author doesn't intend. The writing ability of the author and the reading comprehension of the reader can totally wreck the communication. The faceless nature of the medium makes it easy for the reader to read the most hostile intent into the message, and the absence of the reader when the author is writing makes it easier to write things that you wouldn't say to someone's face.
If someone doesn't understand a point you're making when you're talking face to face, they can interject and ask for clarification. They can see the tone of the communication on your face and hear it in your speech inflection. You can read someone's facial expression as they hear what you're saying and have an idea of whether or not they understand you. You can have a back-and-fourth to ensure you're both on the same page. None of that high-bandwidth, low latency communication is present in writing.
If someone doesn't understand a point you're making when you're talking face to face, they can interject and ask for clarification. They can see the tone of the communication on your face and hear it in your speech inflection. You can read someone's facial expression as they hear what you're saying and have an idea of whether or not they understand you. You can have a back-and-fourth to ensure you're both on the same page. None of that high-bandwidth, low latency communication is present in writing.