Easy. The Allied insistence on on conditional surrender. This terrified the Germans and helped keep Hitler in power. Of course, any “surrender” that kept the Nazis in power should have been rejected.
Harry Dexter White, Undersecretary of the Treasury, was a Soviet Agent. He was the author of the policies that led to Pearl Harbor, an event which greatly aided the Soviets. He was also the author of the Morganthal Plan, a plan to deindustrialize Germany after the war. The Morgenthal Plan was a boon to the Nazis, and Goebbels was happy to publicize to stiffen German resistance in the West. Absent the Morganthal plan, German resistance in the west would have been much reduced.
unconditional surrender
The Allies decided on unconditional surrender before they had gotten to the concentration camps. So it was just as well they took their time grinding the Germans down and not letting them have “stabbed in the back” excuse they conjured up after WW1. As it was, we would have probably nuked them before the Japanese if the war had still been active in Aug 45.