Several factors: Pinochet simply lasted a long time (nearly two decades) and was easily recognizable with his trademark snarl, little moustache and dark sunglasses. In Guatemala, Romeo Lucas Garcia took power in 1978, then was replaced by Rios Montt in 1982, who was replaced in 1983 by Mejia Victores, who was replaced in 1986 by Vincenzo Cerezo... None of them lasted enough to build up enough name recognition in the First World.

Also, there is the Chilean dictatorship's charming habit of assassinating its opponents outside Chile, the most spectacular example occurring in 1976 in the heart of Washington D.C. (!!) when the Chilean secret service killed Dr. Orlando Letelier, a well known opposition leader, and Ronni Moffitt, the 25 year old American wife of his secretary, with a car bomb. The FBI soon determined that the Pinochet regime was responsible. This sort of thuggery in full view of the world's press tarnished the regime's image badly.

Probably the most important factor was the size, composition and residence of the Chilean exile community, which contained many vocal and highly educated people (who spoke Spanish, French, English) who left for Canada, Sweden, the U.S., Australia and publicized the misdeeds of Pinochet. In comparison when the Indonesian government slaughtered the Communists in 1956-66 (half a million dead in 12 months!), the few PKI members who escaped fled to China or behind the Iron Curtain. And very few Western journalists speak Indonesian. That's why you've never heard about it.