Producing tons of equipment is one thing, having trained and effective soldiers to use it is another. The US had to go from basically a border police force to a 5-6 million man army in a very short time. Then the western allies had to get their armies somewhere where they could engage the Germans using their numbers and equipment to overwhelm them. North Africa and Italy really did not provide that kind of an arena, Northern France did, but amphibious landings are not easy and require much planning and equipment of a specialized nature. AND the Allies were fighting Germans, some of the best soldiers in the world!! Just a few thoughts. Best wishes.
John W. Howard