Latin American has had a history of unstable democratic governments and stable authoritarian rulers. Both forms of government are inherently weak to outside influence. The difference is that almost all authoritarian rulers were backed by larger world powers. Mainly the Soviet Union and USA, in a set of proxy wars to gain influence among other countries in the Cold War.
The Soviet Union mainly funded communist revolutionaries in the Americas to have a foothold on the hemisphere. The USSR would then be able to threaten the US with nuclear strikes just like how the US was doing to the Soviets. The most famous example of this is when Fidel Castro overthrew the US backed dictator Fulgencio Batista. He was originally backed by the US until changing sides to the Soviets, which would lead the the Cuban Missile Crisis.
The fear of communist influence in the Western hemisphere would lead the US to overthrow any leader it could that showed the slightest hint of socialism, even if they held similar values. After overthrowing a possibly socialist leader the US would also take advantage of the region economically, and agree upon unequal deals to take advantage of the resources in the region.