There are alternative motivations that have nothing to do with economics of the Saudis as a whole, no NO economic theory, even if it is correct, can explain their actions.
Economics has well-established ways to model non-financial incentives that people value. A simplistic one is to assign a dollar-equivalent.
For instance one could assign a dollar value based on the current value of Saudi investments, an estimated value of managing to remain in power, and an extremely large estimated value of remaining alive. Now the economic model that we have for the Saudis will show a desire to walk the tightrope until their lives come under serious risk, at which point they'll bail.
The example may seem silly, but similar types of analysis are frequently done by economists who are trying to apply economics to public policy questions about things like the environment.
Cheers,
Ben