Why are only 50 pilots worldwide certified to land at Bhutan's Paro airport?

Only 50 pilots worldwide are certified to land at Bhutan’s Paro International Airport, nestled 7,382 feet above sea level between Himalayan mountains as high as 18,000 feet with a single runway. The airport, accessible only to smaller aircraft, requires pilots to have ability to land without radar guidance. Unpredictable weather and thinner air also pose challenges for pilots.