This topic was recently discussed on Visual Politik channel on youtube.
Given the lack of a large single entity posing an existential threat to the nations of this continent as a whole, I can't personally see the need a combined military organisation.
The expansion of military budgets throughout most of Latin America is also unfeasible, due to the perilous states of so many economies in this region.
Lastly, the security threats to Latin tend to be of a more internal nature, which is a matter for policing and counter-insurgency action.
