Answer:
The answer lies in the preventive measures the Incas took to avoid its discovery. The Incas left the site one hundred years after they made it in fear that the Spanish settlers would find it. As they descended the mountain, they burnt the forest trails in order for the paths up to the site to be completely destroyed
Step-by-step explanation:
However, from the picture above we can say it's as a result of majority of their tribesmen being wiped out and no written language to pass along the directions/descriptions of Machu Picchu