Why do all the honest, decent, socialist presidents/leaders get inated/overthrown and replaced by s?

Jacobo Arbenz Guzman, Patrice Lumumba, Daniel Ortega (though he's in power again) Salvador Allende, Thomas Sankara, Mohammed Mossagdh, Leon Trotsky, Che Guevara (the strict exception to the rule)--the list goes on and on.