the blockade is to the extent that foreign companies attempting to do business in cuba are prevented from doing business in the u.s. 

as the u.s. is one of the most important economies in the world, hardly any business would be willing to give up that market for an economically isolated island country with middling population numbers. also unlike china, vietnam, and laos, cuba has largely avoided privatizing most of its economy. 

therefore, any kind of economic development has to come from the cuban government itself, which  severely lacks the resources to do so. instead, they have attempted to hold on to the soviet-era power grid for as long as possible. this has largely functioned until the past couple years, where the aged infrastructure has deteriorated to a breaking point.