remember in 80 & 90s FATA was the most peaceful area in the country regardless of all the halla-gulla in Afghanistan , but after the 2001 US attack it blown up because the tribal system of governce and Pashtunwali (the ancient code of life for Pashtun) was broken.
secondly, US/Europe/China/Russia .. err all the major powers have stake in the stability of Saudi Arabia not just because of oil but also Mecca/Medina and influence of Saudi’s on ordinary Muslims as far as Brunei.
From the Islamists point of view, its stable because of Land of Hejaz - wallah o alam