The grizzly bear in the room is the US. Since 1823 the Monroe Doctrine has been central to US policy. The doctrine states that the US will resist any foreign intervention in the political affairs of the Americas with the Americas being North and South America along with the Caribbean. Over the years the policy has waxed and waned in favour but never gone away. I don't know what the state of it is at the moment but the US have been pretty vocal about non South American, North American or Caribbean support for Venezuela.