Presumably because they can't do anything about it. The US offers Cuba a nominal sum to "rent" the land to maintain legitimacy and iirc the Cuban government has continually rejected it on principle.
I'm imagining a huge stack of checks in a storage room. When the time is right, the cuban president will deposit them all at once, overdrawing America's account and collapsing the economy.
Cuba one million percent doesn’t want them there, it’s just they can’t do anything about it. Taking it back militarily would definitely trigger war / an invasion. It was created when Cuba was conquered and colonized by the USA.
Cuba was a US territory for a couple of years at the start of the 20th century after they took it off Spain in the Spanish-American war. It got independence as a puppet.