Why does no one know where Moses is buried?

The chapter doesn't give a reason. It says where, in general, and what isn't known: "He buried him in the valley in the land of Moab opposite Beth Peor, but no man knows where his tomb is to this day" (34:6). Other burials in the Law are often told with their places: Jacob set up a pillar on Rachel's grave, "The same is the Pillar of Rachel’s grave to this day" (Genesis 35:20), and of Aaron Deuteronomy says, "There Aaron died, and there he was buried" (10:6). The New Testament mentions Moses' body once: "Michael, the archangel, when contending with the devil and arguing about the body of Moses, dared not bring against him an abusive condemnation, but said, ‘May the Lord rebuke you!’" (Jude 1:9). Jude says no more about it, and Deuteronomy says no more than 34:6. Any reason given for the unknown grave goes beyond what the text says.