Because Ike had no combat experience and wanted a "safe" strategy.
I would think that it was more of a political decision than a military decision.
But, what was the desired political outcome?
-——The Allies advance on an extremely large front. Why?-——
Isn’t there usually more than a single reason for any decision, especially a military decision?
As I recall, there were lots of things going on here . . . supply issues, troops that had run out of momentum, a tough slog across the Rhine up north, some hope about internal disintegration of the Reich, the Russian situation, the continued bleeding and total deterioration of the Luftwaffe, ugly results in Normandy with an expected fast armored thrust that didn’t work out, etc.
The Allies advance on an extremely large front. Why?
Because Ike had no combat experience and wanted a “safe” strategy.
Is there anything wrong with a “safe” strategy?
Victor Davis Hansen has a brilliant observation about the Allies strategic bombing campaign.
It forced the Nazis to pull tens of thousands of the best weapon they had against the Soviet tanks, the 88 cannon, and use them against our bombers.
Our bombers as targets paved the way for the Soviet tanks to take Berlin.
The “Broad Front Strategy” was picked by the western allies for a couple of reasons:
1. Politically it was easier. By not selecting a single allied army, American/Canadian/British, it was easier to get all the allies to cooperate.
2. The western allies were just not up to mobile warfare on a large scale. A penetration on a narrow front can be cut off and surrounded and the army lost.