The US doesn’t block anything except for it’s own companies/interests to work with Cuba. That’s it.
And I don’t find it impossible for a country to be incompetent… Nor do I find it unreasonable for a country to be self-isolating.
The USA embargoing it certainly sucks for them. But that’s how it goes. But even to that point…
Despite the existence of the embargo, Cuba can, and does, conduct international trade with many countries, including many U.S. allies; however, US-based companies, and companies that do business with the US, which trade in Cuba do so at the risk of U.S. sanctions.[10] Cuba has been a member of the World Trade Organization since 1995.[11] The European Union is Cuba’s largest trading partner, and the United States is the fifth-largest exporter to Cuba (6.6% of Cuba’s imports come from the US).[12] The Cuban government must, however, pay cash for all food imports from the United States, as credit is not allowed.[13]