Because of Hitler's attack on Russia. Operation Barbarossa. Then the Allies signed the agreement to let the Russians in first, the 3rd Army was there first, but had orders to pull back 50 miles, and let the Russians move in, and watch. My papaw watch in horror as the Russians Raped, and burned, murdered, pillaged their was into Berlin. He hated his Allies buddy's. He was only 18 years old. So it was , not good will. Americans and the Brits didn't trust the Soviets and they gave them what they wanted to just appease them.