Why did the Inca not have writing even though the Maya and Aztecs did?

Inca did not have any writing to fulfil the purpose of communication and store knowledge as Mayan and Aztec people did.  

Explanation:

The Incan culture is one of the mysterious indigenous civilizations in South America. The Incas did not possess any alphabetic letter system but had the Quipu. This Ouipu was a unique and portable system to store various data in civilization. Incas used several colourful knots to use the Quipu system.  

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