It was stable because anyone who objected to his rule was executed or disappeared ffs!
https://en.wikipedia.org/wiki/Cuban_dissident_movement
"According to Human Rights Watch, the Cuban government represses nearly all forms of political dissent."
"The island was the second largest prison in the world for journalists in 2008"
"In 2012, Amnesty International warned that repression of Cuban dissidents was on the rise over the past two years, citing the Wilmar Villar hunger strike death, as well as the arrests of prisoners of conscience Yasmin Conyedo Riveron, Yusmani Rafael Alvarez Esmori, and Antonio Michel and Marcos Máiquel Lima Cruz.[18] The Cuban Commission of Human Rights reported that there were 6,602 detentions of government opponents in 2012, up from 4,123 in 2011."
Yes, political repression is certainly bad - not disputing that. However, the average Cuban couldn't give a damn, as most people couldn't give a damn about politics. The fact remains is the average Cuban is far better off than the average Haitian, they enjoy very little outgoings, excellent healthcare, free utilities.