Why should Communist countries be continously ruled by dictators?

Communist countries seem to have a fetish for continuous rule by dictators.

Fidel Castro, of Cuba, is one such example.

People should, normally be fed up with a President or a Prime Minister or a dictator within 10 years, maximum.

People, will definitely elect a different ruler, if free and fair elections take place. Even in dictatorship of proletariat (Workers' rule), there is scope for competition to be rulers. Why this is not happening at all in Cuba?

China too seems to have a similar problem. Leaders change very rarely, there also.

Why should people patiently wait till leaders become too old and get forcibly shifted to their tombs?

Some of my acquaintances and friends tell me that Cuba had, and is having the best possible rule, which is not available in Capitalist countries. But this ideal administration can happen even if there is change of leadership (not hereditary).

North Korea is another country where leadership took place only after the death of its dictator and the change was only hereditary.

What is happening in North Korea and Cuba, nobody knows.