The Germans, especially in 1942, did in fact attack merchant shipping directly off the east coast of the United States. A total of 127 ships were torpedoed and another 14 were shelled, for a total loss of 141 vessels to enemy action. Indeed, early U-Boat efforts were so successful that the period after America entered the war has been referred to as the Second Happy Time, in reference to the Happy Time of 1940-41 in which so much British shipping was sunk.

Why did they not attack ports directly? I would say it's down to a combination of lack of ability to do so, and the extreme risk of attempting it. A Type IX U-Boat (the only one long ranged enough to easily operate in North American waters) was primarily armed with torpedoes, which would be entirely ineffective against port facilities. In addition to these, it had a single 10.5 cm deck gun, a light artillery piece similar to those mounted on destroyers. In no way was it equipped to shell major land targets, and had it attempted to do so, it could only have caused minimal (and easily repaired) damage to facilities.

Then there's the risk. One of the primary reasons the U-Boats had such success off the US east coast in 1942 was that American coastal cities failed to enforce night light discipline. This meant that U-Boats could sit on the surface (they could only submerge for brief periods of time) in the shadows and attack lit-up targets either emerging from the port or following the coastline. To go in and attack the port itself would mean exposure of the U-Boat. Aircraft and/or surface vessels would be summoned and the submarine would likely be hunted down fairly quickly.

Thanks for the insight

Can i ask a follow-up... How were Blackouts enforced, or were the voluntary?

How did the gulf and the east coast differ in this?