The Jones Act can be broken into 3 parts:
1. transported on ships that are built
We want to maintain domestic shipyard capacity and not have the only shipyards be those that are government contractors. Why? Imagine if we are ever in a situation where we need Liberty Ships again.
2. transported on ships that are owned,
We want to both protect domestic owners as well as be able to hold them accountable if they screw up. You sometimes hear stories about ships abandoned by their owners and the crew forced to stay on the vessel. Or abandoned cargo such as the fertilizer that caused the Beirut blast. We want to minimize those situations.
3. transported on ships that are operated
We want the people working the ships to be invested in our country and we want to maintain a population with these skills. Why? In the event of a Liberty Ship situation, you need people to crew them. But also accountability, who is more likely to report the captain ordering waste oil to be dumped overboard: A US citizen who knows the rules or a sailor from Indonesia whose passport is being held by the captain?
There is a large amount of intercostal and waterway shipping that takes place in the US, grain down the Mississippi, steel on the Great Lakes. Do we want that to be open to Iranian or North Korean ships?
Lastly, the Jones Act only applies to goods shipped between US ports. So if Hawaii is buying Russian gas from Russia, as long as the ship goes from Russia to Hawaii the Jones Act doesn't apply.