I first learned about the Jones act while reading about cruise ship port destinations (since most cruise ships have flags of convenience, a notable exception being the cruise ship based out of Hawaii for Hawaiian ports).
Its a relentlessly efficient industry and I don't think a lot of Westerners are willing to spend an entire year on a cargo ship. The Jones act is actually an admission that the US cannot compete.
This doesn't stop nearly as many people/companies as much as I wish it would.
This prevents someone from say dropping off all their goods in Miami, then letting a British liner pick them up later and drop half off in NYC, and the other half in London.
Instead you have to either ship it yourself to NYC and Miami, or you have to send it by train to NYC from Miami.