They are debanked from the global financial system due to US sanctions on any business who trades with Cuba

They can’t trade in US dollars, the global currency that nations most typically use for international trade

They can’t follow normal shopping lanes because boats going to Cuba have to stay away from US ports for 180 days

Any company can be sued by any American alleging they have benefitted Cuba

Also, the United Nations has voted unanimously multiple times to drop the sanctions on Cuba- only USA and Israel vote no. To say that it’s a myth that Cuba has been adversely affected by the US actions is plainly stupid.