The conference at Yalta had already pieced out post war Germany, where it was determined that the Soviets would govern east Germany, and the western allies would govern west Germany. Berlin itself had also already been partitioned as part of the Yalta conference and Berlin was within the Soviet Zone (East Germany) The western allies saw no need to "race to Berlin" and suffer additional unnecessary casualties. The terms of post war Germany had already been established.

edit: It is also important to note that the Soviets were much closer to Berlin than the Western Allies during the Yalta Conference, and the Soviets had also suffered a vast majority of the casualties in defeating Nazi Germany. They were in a far more advantageous position to dictate the terms.