Why did the Nazis have such a technological advantage in Wolfenstein: The New Order?

The Nazis didn't develop their advanced technology - they stole it from the fictional Da'at Yichud. The Da'at Yichud are a secretive sect of scholars who tirelessly work to create highly advanced technology, and have done so throughout human history. The caveat being they believe that the act of creation alone is enough - these inventions were never intended to be used. General Deathshead stumbled upon one of many technological caches, and pilfered what he found there for his own purposes. Some of the technology has been reverse-engineered by the nazis, which was enough to give them their huge technological advantage seen in game.