The Jone's Act is all about keeping America's ship-building industry alive. Without it, no ships would have been built in American yards, too expensive compared to buying ships built in Asia. Without it, even the ship-builder "Newport News" wouldn't be there to build our Navy ships.
The American shipping companies have abused it and created a monopoly for themselves. Lykes Lines used to ship direct to Alaska, and then continue on to Vancouver B.C., then to Seattle and Portland. The barge companies apparently made a deal for Lykes, and the other shipping companies, to ship direct to Seattle and Portland. So we pay 5k for a container to Seattle, and another 5k to have it reshipped to Alaska. Hawaii has the same problem. California shippers are playing the same game on them.
It's not the Jone's Act which is at fault, it's the scheming American shipping industry taking unscrupulous advantage of it.