There isn't a compelling reason yet to invade, they're still willing to sell to us and they aren't mining water preventing us from receiving oil from other people.
It's not that, you would need to HOLD the oil fields and govern the region. Status quo is the only acceptable choice at the foreign policy level. Americans who consider themselves the best of the best work every day to service the kingdom.
Sure and Apple even has even found a replacement CEO for him. But my point is that leadership can be removed (or die) and the organization will still be around.
MBS is well aware of USA using either a coordinated attack (OBL raid) or a targeted strike (cruise missile) to kill high level targets. Perhaps Saudia Arabia will continue to exist as a country after a war with the US; but he won't and the US will be getting the oil.