When you look across history, pretty much any society with enough trade to require bookeeping and stratified enough to support kings will have developed (or borrowed) some kind of writing.
The Advanced culture in Peru and the Andes in South America was too isolated from other such societies to borrow their systems, so what they came up with on their own was probably the world's most interesting (if not practical) writing system: Quipu, which consisted of strings colored and knotted strategically to communicate information (numeric certianly, but many argue much more).
The only other pre-columbian drawings in South America I'm aware of are the Nazca lines from southern Peru. They are rather odd, in that they cannot really be properly appreciated from ground level (although there were typically hills nearby from which they could be appreciated by their creators). There are a lot of theories about what they were for, but few of them include information storage, like you'd get with a proper writing system.
The reason for this being the only writing system known in South America is probably relatively simple: The Andean area contained South America's only real advanced civiliation (The Inca by Pizarro's time).