The city that we know as Machu Picchu was discovered by American professor Hiram Bingham in 1911. He was looking to follow the path of a Spanish conquistador, and came across the ruins of the city. The name is a retronym based on a nearby mountain, because the real name of the city is lost. Machu Picchu in Quechua means “old mountain”.
Since the capital of the Inca empire was Cusco, Machu Picchu is not as special. However, since the Spanish colonists never found (and thus never attempted to destroy) Machu Picchu, it was preserved.
The locals have a little beef with Hiram Bingham, because he took all the remains he could find as well as 40,000 artifacts back to Yale.