Being a doctor in Cuba is often seen as one of the most respected professions, but financially, it can be a very different story. Medical education is free, but doctors work for the state and receive extremely low salaries compared with what their profession would normally earn elsewhere.
They also face shortages of medicines, equipment and basic supplies, making it difficult to properly treat patients. Imagine how desperate that makes them feel. Many doctors eventually leave the country or seek opportunities abroad because their salaries are not enough to afford basic necessities.
Cuba also sends large numbers of doctors abroad through its international medical programs, with the Cuban government receiving pretty much all of the money paid for their services.
So you can spend years studying to become a doctor, only to end up struggling to afford the same basic necessities as everyone else. You're better off selling those potatoes you grew on your backyard.