Good question! Rabbi S. R. Hirsch provides an answer, stating that no humans were involved in the burial of Moses so that no one would know the location of his burial site. God knew that if Moses’ burial site would be known it would become a place of pilgrimage, and ultimately it might even cause people to pray to Moses as if he were a deity.
All that we know of his burial site is what is written in the Torah:
And Moses went up from the plains of Moab to Mount Nebo to the top of the summit facing Jericho. And the Lord showed him all the Land… And Moses, the servant of the Lord, died there, in the land of Moab, by the mouth of the Lord. And He buried him in the valley, in the land of Moab, opposite Beth Pe'or. And no person knows the place of his burial, unto this day. (Deut. 34:1, 5-6)
The Mishna (Avot 5:8) teaches that this burial place was created at the close of Creation, during the twilight period between Friday and Shabbat. The Maharal of Prague explains the significance of this teaching. He writes that this interval belongs to both the natural order of the weekdays and the otherworldly zone of Shabbat. This special combination befits the unique nature of Moses, in his life and in his passing. Similarly, Moses is called “the man of God” (Deut. 33:1), since he was a mortal man who nevertheless attained Divine heights; one who dwelt in “two worlds”, as it were.
As a “footnote” it is interesting to observe that many claim that the English expression “the kiss of death”, a quite negative concept, is based on the verse that states how Moses died by the “mouth of God”. Rashi, based on the tradition of our Talmudic Sages, explains this to mean “with a kiss”. Therefore, “the kiss of death” in the verse is clearly a sign of love, from God to Moses. And this expression is used nowadays in Hebrew — “mitat nishika” — “death by a kiss (from God)”, to describe a painless and merciful passing from this world.