Registering a ship in Panama , Bahama , ( used to be Libya, but not now) isn’t about the taxes completely, it’s also about the certification and annual inspections which cost millions on certain vessels. You risk having to limit trade in the Great Lakes because you can’t pick up frieght in an American port and deliver to another American port on a foreign flagged , or even not US built ship, that under is under merchant marine law , also known as the Jones Act. It’s to protect the US ship industry, you can’t go from Miami to porto Rico on a foreign flagged vessel with cargo.
Weirdly many Great Lakes freighters cannot operate in the ocean . They are too long , they are purpose built and the wave lengths in the ocean would break them up . The cruise ship dodging in and out of US waters , like an Alaskan cruise is because the Casino ( on every cruise ship) and the duty free shops on board can only operate in international waters , not licenced in port and that’s where cruise ships make millions .
I know off topic but I’m fascinated with maritime law and weird stuff like when a boat hits a pier , it’s not a collision, it called an allision. Whole other vernacular, and insurance process .