[HHest]

Which of the "other communication modalities" do you have in mind? Because I do not see how writing can reproduce this "interactive value".

Of course, the writer can try to anticipate questions and capture as many facets as possible, but the more comprehensively one does that---for example by covering both elementary and complex queries from all possible audiences---the more likely that one ends up with a mess of an essay that few would want to plod through.

In addition, the readers, having no chance to pose questions, often ends up having to make a judgement call about the validity of the argument based on the limited case presented in the writing.

Note: a dialog conducted via the written words does not really count, because interaction is still there, albeit less immediate than a direct exchange. And in such cases, the people who read the written record of this dialog would not get so much out of it as the two original participants, again due to the lack of interaction.