Factual error: Whenever you see a license plate, it says "Puerto Rico, Isla Del Encanto" (where the film was shot). The movie takes place in Cuba.
Factual error: During the opening credits, as the car is driving to the hotel, the Faro de San Juan and Castillo San Felipe del Morro are notably visible in the background; this is one of the most recognizable landmarks in San Juan, which doubles as Havana in this movie. Although there is a similar fort in Havana, the San Juan lighthouse is distinctively different from the Havana one.
Answer: Because they were singing revolutionary songs. And at that time was strictly forbidden.