Long story shot, he had no way to get a sufficiently sized army there, no way to keep them safe while there from being cut off, and not really a large enough merchant marine to keep them supplied.

The Kriegsmarine in the Spring of 1941 combined had a strength of 3 BB's/BC's and the recently commissioned Tirpitz which was still just becoming combat effective, along with just 4 remaining heavy cruisers, 5 light cruisers, and about a dozen destroyers. The recent Norwegian campaign had badly bled her surface force, in particular about half her destroyers were sunk in 2 weeks worth of action.

Meanwhile the US Atlantic Fleet comprised at the time 6 Battleships, the older dreadnoughts of Battleship Division 5, and the 3 modern standard types of the New Mexico Class fresh from the Pacific as Battleship Division 3. About a dozen cruisers, some older, some modern treaty cruisers. And about 2 dozen destroyers as escorts.

While nominally the USN's "Neutrality Patrol" was just that, it was really meant to favor the British, aiding in escorting convoys and helping the RN do more with their stretched manpower, by September of 1941 the USN would be under orders to fire on any Axis ship that entered the Western Atlantic unannounced or invited or threatened any ship under escort.

On top of the surface asset though were the carriers, 2 fleet carriers were in the Atlantic at the time, the USS Wasp, and the USS Yorktown. As well as the smaller older carrier USS Ranger.

SO while distributed the USN had the ability to coordinate, concentrate, and harry any hostile task force which would have no safe haven close at hand or air support of their own. And in 194 the USN was of a mind to shoot first ask questions later.

We would also be foolish to assume any sort of surprise would be possible. In the summer of 1941 the Germans tried to get just 2 fast warships through to the Atlantic, not only was the Royal Navy aware in advance due to intel, but deployed to screen for them, and was able to find, bring to battle, and destroy them. Any task force of sufficient to get to the US in force would have brought out every warship the formidable RN had to offer to do battle. A to the British eye it would jut a easily look like some suicide attempt at Operation Sea-lion.

And finally is the logistical aspect. Germany simply didnt have the shipping at hand to get the job done. Her merchant marine had rebounded after WW1, but it wasnt the same, and much of it was abroad when war came and thus impounded and of no use, while what wa captured was not enough, and her ships were always targets of allied raids anyway.

Thus her slow lightly armed transports would need constant escort to first land troops, then a continual supply of more men, more equipment(spare parts, ammo, tools of war, food stuffs if enough was not to be found through forage, with wounded men evacuated, all while under attack by sea and air).

The Japanese, with a much larger navy and merchant marine looking at a similar question pronounced even a small invasion of the Hawaiian islands beyond their ability, with many doubting even Midway could have been held if captured.

As crazy as it may seem, a bloody slog through the Russian muds and snows was the more feasible option.