There are restrictions to traveling to Cuba because of failed "diplomatic relations" between "Cuba and the USA".
EXPLANATION:
During 2016, American diplomats mysteriously fell ill in Cuba and President Trump accused Cuba of being responsible for the mysterious illness.
Also, in 2018, Cuba was one of the few countries that supported Nicolas Maduro, the president of Venezuela while the US along with several other countries was trying to overthrow him.
This led to tensions between Cuba and the U.S. and Trump restricted the travel to Cuba.