QUESTION OF THE 3RD PERSON NARRATION

If the five Deuterocanonicals were believed and said to be written by Moses, why was there a Third (3rd) Person Narration of the various biblical events recorded?
By 3rd Person Narration, we mean that instead of Moses who was said to write the Books of Genesis, Exodus, Leviticus, Numbers and Deuteronomy to refer to himself as "I" or using the pronoun "I" to represent himself over things he encountered by direct experience, a third Person is doing the storytelling or narration.
For instance, instead of Moses saying or writing, I was here and there doing this and that, and God told me this and that, or God said to me that I should strike the rock, etc., someone else, a 3rd Person is rather saying or writing on behalf of Moses, for instance, "And Moses went up the Mount Sinai, And Moses lifted up his staff, And Moses died, etc. Who is this person that is writing, telling or narrating the story as a Third Person when Moses was said to be the Author of the Five Deuterocanonicals?

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