It shouldn't be but there is an undeniable legacy of US foreign policy, especially since the latter half of the 20th century, having its fingers in several pies in both central and southern America.
You are correct in saying that the USA shouldn't be the world police but your elected executive have at times taken it upon themselves to stretch their 'influence' to their continental neighbours; whether it's having a CIA agent as the President of Costa Rica (Jose Figueres, terms 1948-49, 1953-58 and 1970-74 admitted as much in 1981), the financing of anti-Sandinista groups in Nicaragua and the associated atrocities committed by the Contras as well as the political fallout of the Iran-Contra affair, the assassination of CiC Rene Schneider and the subsequent coup d'etat by Augusto Pinochet in Chile or the long-standing asymmetric civil war in Colombia with right-wing paramilitaries having initially received extensive support from the USA, to say that the United States, for whatever reasons or goals, hasn't had business in central American and beyond is wilful ignorance.
This isn't a perfect analogy and I won't pretend it is but I see at least some similarities to colonial legacies in the United Kingdom, France and Belgium; decades or centuries of interference, influence, invasion or however you describe it, in a foreign land and then surprise when the people of those lands try to go to the source. "They've been trying to impose their 'better life' on us, so why not go to the source and chase that better life for ourselves?" could be the mentality one has in these situations.