Why was the Malaysian MH370 flight not detected by the Diego Garcia US Naval and Intelligence Base in the Indian Ocean?

Diego Garcia is a tropical, footprint-shaped coral atoll located south of the equator in the central Indian Ocean.

It is part of the British Indian Ocean Territory, but now under US Control under lease from UK.

The American military base on the island of Diego Garcia is one of the most strategically important and secretive U.S. military installations outside the United States .... http://intellihub.com