The United States has such a large GDP because 1/3 of it is the private healthcare industry. Another massive chunk is the government throwing tax dollars at a shell company of a shell company of a shell company that moves a government contract for construction around to each other 4 times, all subsequently increasing GDP.
Well, that really isn’t all of it. The majority of the logistics is done at sea with larger vessels that offload onto smaller boats that take it to this pier. That is most of the pier though, although there is (was) a little more to it. There’s an anti-missile weapon system near the shore. This was the wrong thing to build though because the seas are really rough there and there’s no natural harbor, so they really should have gone with a much more stable structure.
If you’re interested in more information, this guy does some really good detailed videos on this subject, and also almost any other involving shipping.