[thiagoharry]

Cuba is an island with very little natural resources. Therefore, to build almost anything, it needs to buy it from other countries. The sanctions makes everything coming from outside much more expensive. And to buy things, they need money (dollar, or some other international currency). They can get it only in the few areas where they can be internationally competitive (as any imported product is much more expensive to them, they will not be competitive in most industries): tourism, offering medical services and selling cigars.

As they have fewer baskets to place their eggs, they are much more succetible to crisis: a blow in one economical activity generates crisis that affects a lot all other areas. For example, one of the causes for the current crisis is the pandemics that dropped their tourism to zero for 2 years. Now they have much less to invest, affecting all economical activities.