It is not Nathan's story. He is overconfident, pushy, and self-absorbed. He expects to be listened to, but rarely speaks WITH anyone...only AT them. The story, therefore, is told from the points of view of those who are most effected by his decisions. His wife and his four, vastly different and interesting, daughters. They are, in essence, prisoners of the household as they are held captive by his attitudes and decisions. He is very chauvenistic evne to the point of misogyny. He is quoted by one of the daughters as saying sending daughters to college was like pouring water in a good pair of shoes--you either watch the water pour out of the shoes, or you are amazed the shoe held the water but suffer from water damage. He is a coarse and hateful man, and therefore does not have a voice in the story. His voice has caused enough damage.
I'd like to add another insight for why Nathan isn't given a voice. The narrator(s)the author chooses to tell the story gives the reader a clue as to what message the author would like us to take from the story. By having his wife and daughters tell the story, we know it's the effect of Nathan's behavior toward his wife and daughters that is significant in the story. If Nathan were given a voice, then perhaps the importance of the message would lie within Nathan's mind, history, and behavior. The author would be exploring how Nathan reached the point of being willing to treat his family as he did.
As a teacher, I might ask my students to write a part of the story from Nathan's point of view so they can see how it changes the story.
I suspect it is because Nathan does not listen to anyone else, his innermost feelings are not known, and thus, the story is told through the eyes of his daughters and his wife, Oleanna.
The women of the Price family are left to figure out why Nathan acts as coldly and cruelly as he does toward them, and why he would risk the lives of his family in the Congo.
Here is an excerpt from the Character Analysis section here at eNotes that may shed further light for you as to why the male voice remains silent, except through interpretation:
"His experiences during World War II made him "contemptuous of failure," and caused his "steadfast disdain for cowardice [to turn] to obsession." He had narrowly escaped the Death March from Bataan during the war, which claimed the lives of all the men in his unit except his because he had been evacuated due to an injury. Since then, he has carried the guilty suspicion and the fear that he was a coward, believing that God was always watching and judging him. As a result, he determined to prove his worthiness by saving more souls than were lost in his company. He "felt it had been a mistake to bend his will, in any way, to Africa," and so he became harder as time passed there. His monomania-cal pursuit of salvation for himself and the villagers blinds him to the dangers he and his family face, and so he refuses to let them leave."
Bängala is poisonwood. Bangala is God. Nathan would shout, "Tata Jesus is Bängala" (533). The Poisonwood Bible, came from a man "who believed that he could tell nothing but the truth" (533). You can't go into another culture and expect them to bend to your beliefs because you believe you are superior, because you are more advanced. You go into a different culture and mold yourself to what has worked for them for hundreds, even thousands, of years, and you listen.
Kingsolver is absolutely brilliant. The book is titled The Poisonwood Bible, and it consists of different books named from the actual Bible. The Bible records the strife of man and his relationship to God, and the Prices have survived the jungle with and without God. This is the Poisonwood Bible that Nathan rewrote.
Whenever there is a mistake in the Bible, they title that Bible by its mistake. Nathan made the mistake of being stubborn and arrogant towards a culture that he did not understand. The women are like the prophets, and Nathan was their god. In the actual Bible, God does not write it himself, so in the metaphor, Nathan likewise has no voice.