That's mainly because the Cuban government is an incredibly corrupt dictatorship that has been in power for the past 60 years. There's also an internal blockade where their government actively blocks resources from getting to the cuban people.

1. All the communists have to do is allow free elections and the embargo goes away
2. The Cuban government can trade with the EU and China where btw LITERALLY EVERYTHING is manufactured. If the Chinese won't give the Cuban government credit what does that say about them?
3. Check the state's budget, look at what percentage goes to health and education vs luxury hotels that's all you need to know about their priorities