In Things Fall Apart, why does Chinua Achebe mainly focus on the tribal traditions and beliefs?

I would argue that it is reductive to say that Chinua Achebe focuses mainly on tribal traditions and beliefs. Indeed, Achebe covers a number of interesting subjects in his debut novel, one of the most important pieces of postcolonial African literature ever produced. With that being said, Achebe does incorporate a lot of traditional aspects of Igbo culture into his prose. He does this in part to properly tell the story of Okonkwo, a tale that would otherwise be disregarded, marginalized, and ultimately overlooked by Western narratives (much like it is at the end of the novel). Achebe highlights traditional Igbo beliefs in order to juxtapose them with the Western conventions that invade Nigeria as the novel progresses. Achebe's use of Igbo culture and traditions enables him to present an authentically Nigerian tale for an English speaking audience.