Why? The jihadis are actual a threat to the Saudi's existence. The jihadis want nothing more than to rule over their holy land.
Some jihadis are a threat to them, but I wouldn't say all. Wahhabism is the theological backbone for many jihadi groups and for decades Saudis disavowed knowledge of many of these groups while quietly pumping their coffers full. Many of these men know their bank balances down to the penny (I heard the stories from their kids/relatives at school in London) and all of a sudden they either can't account for a couple million and/or they are duped into giving millions to a front charity for a militant group?

While I don't doubt there are many Saudis- even in the royal family and government- who are legitimately trying to do their part, I'm not quite convinced everyone is on board.