Why were Bailey and Maya sent from Stamps to LA?

Maya and her brother Bailey are raised in Stamps, Arkansas by their grandmother, whom they call "Momma," after their parents abandon them. Momma runs a general store in town, whose revenue she uses to provide for Maya and her brother. While Momma takes care to support Maya and Bailey financially, she cannot stifle the overt racism that is rampant in the town. A turning point of the novel is when Maya's grandmother takes her to a dentist, who refuses to treat Maya on account of her race. Soon after, Bailey witnesses a dead black man pulled from a pond by a white man. The white man laughs at the black man's corpse and jokingly threatens to leave Bailey with the dead man.
When Bailey is understandably shocked by the extent of this racist exhibition, Momma is prompted to move to Los Angeles with the children in order to be with their birth mother, Vivian. Vivian and her children finally bond in Los Angeles, where their beautiful and gregarious mother celebrates her children, and Maya and Bailey in turn earn a respect for their mother.