[RPKESQ]

There were many reasons, but the main reason was lack of supplies for the ground combat troops. The Allies could not supply two large army groups with enough for full-out continuous attack at the same time. The reason for this was that the Germans still controlled the ports, so all Allied supplies had to come through the Normandy beach-head.

This supply problem was so great that even after the Normandy breakout, Eisenhower had to continually switch who was going to get the majority of supplies from the Northern Army Group (run by Montgomery) to the Southern group (run by Bradley).

This supply problem was not fully resolved until after the war. Many Atlantic ports were held by the Germans until the final German surrender. Those that did surrender earlier were so destroyed by the Germans as to be mostly unusable.

In retrospect they should have given Patton what he repeatedly asked for, which was all the supplies. By letting Monty be a holding position (the anvil), Patton could have run amok through the Germans as the hammer. But, inter-Allied politics would not have let that happen and at the time it was not as clear to the Allies which was the best strategy. Thats why Eisenhower decided on a "broad front" strategy.

Which might have lengthen the war. Another deciding factor was how fast the Russians could advance. I see no evidence that Germany would have surrendered any faster unless the Russians were able to advance faster (the had their own supply problems).