The Bland Normality of Proper English

An important aspect of any humans life, as well as an important aspect of any novel is dialogue. Talking is something we learn to do in the first few years of our life, and something we utilize until the end of it. No two groups of humans talk the same either, certain subcultures/groups have certain nuances in pronunciation or sentence structure that give that certain dialect a flare. This idea is certainly evident in Their Eyes were Watching God, as all the dialogue from Janie and her associates is written to represent how it would've sounded in person as accurately as possible. However, I feel like this practice is rarely used. In most literature about ethnicities or cultures other than typical "proper English-speaking" Americans, the dialectual flairs that make these ethnic character's speech unique gets literally lost in translation, with each sentence going through the author's head and being written out in as perfect English as the author could produce. I wonder why Hurston chose to intentionally not do that, and what the significance of it is?