Why are zero of these ships US flagged?
There are 118,000 ships in the world. Only 115 are US flagged.
Blame politicians and unions.
[Why are zero of these ships US flagged?]
Maybe so they can get into neutral ports that might bar ships of combatant nations.
Or maybe just cheaper.
Roman Empire ~450AD. Nothing truly Roman anymore.
A U.S. flagged vessel has to be built in the United States and manned by U.S. crews. Steel and labor are far cheaper in shipyards abroad, as are foreign crews.
Congress has sort of made up for this with the Jones Act, which requires that any intrastate shipping be done by U.S. flagged vessels. This has created a bunch of lucrative niches - Hawaii, Alaska, Puerto Rico, Gulf platform supply, coastwise crude and products shipping.
“Why are zero of these ships US flagged?”
Because Congress REFUSES to shut down private sector unions.
Because the only time you flag your ship under these US is if you are shipping within these US, per the Jones Act. Otherwise, you pick a country with no taxes and lax regulations, because foreign shipping operates under it’s flag of convenience, not the port you’re in (within reason). US flags mean you’re at a huge disadvantage for anything going to / coming from foreign shores.