score:12
Because the costs outweighed the benefits. They could fairly easily block submarines entering the Atlantic by then. It served very nicely as a [by the Allies] attackable port where the German Kriegsmarine had parked their ships. Kept them far away from doing any harm elsewhere.
Yes, the Germans could ship iron ore via Norway, but only during the winter. In summer, they could use the Baltic Sea route. That route was the more important one and could not be closed by the Allies.
Of course, the Allies could invade Norway. But at great costs. The possible invasion beaches would be:
Not a place you'd want to invade, unless absolutely necessary.
The Allies had a pretty bad experience, early in the war, invading Norway. After that, they learned at Dieppe that a maritime invasion against a well-prepared enemy was near suicidal.
As it was, the Allies were very happy Hitler believed they would invade Norway. Never interrupt your enemy when he is making a mistake. (N. Bonaparte)
Upvote:2
Because it was Plan "B" (or even "C"). In 1942, Winston Churchill was "undecided" between invading Norway or North Africa, but the Americans tipped the balance in favor of the latter campaign.
Let's look at the results of the plan that was actually followed, the invasion of Italy:
Let's compare that as to what was to be gained by a Norwegian invasion: