Which proves once more that the governments do not really give a flying fuck about people and are willing to keep them in jail like conditions without those people committing any offence.
I believe that the US citizens who working on board could leave, it's the NON-US citizens that the US didn't give a shit about. Hell, keeping the crew onboard meant that the crew will spend their money onboard for necessities like water, cigarettes, laundry and drinks, so that they could make a bank out of bad situation.