There was!

Gran columbia in the early 19th century, created from some newly independent spanish viceroyalties (columbia, Ecuador, a few others). It only lasted a decade or two due to infighting, but bolivia takes its name from the man often credited with uniting it - simon bolivar.

As to why... Well, that could be a book, and a controversial one at that...

http://www.britannica.com/EBchecked/topic/241012/Gran-Colombia

Edit: as to why there isnt a push now, these countries have centuries of animosity and rivalries (ie: argentina and chile) and not especially stable national governments to begin with. Brazil, the most powerful player in the region does not share the common spanish heritage either...