The mountain was/is a religious item for them, I believe.
That too.
Everest = Sagamartha (Nepali) = Great Mother Goddess.
You don't want to go messing around with the Great Mother Goddess unless there's a darned good reason for it, like making more money in a month as a porter or guide than you would in a year otherwise.
Aside from Kathmandu, the Khumbu region is the most prosperous and well-educated in Nepal (Hillary Schools). Trekking and mountaineering are huge money makers for the region. Lots of Sherpas speak competent English, and their physiology gives them a completely unique ability to go to high altitude (5,000 meters++).
The Great Mother Goddess has been very good indeed to the Sherpas.