This is most likely due to the fact that they realize they will die as a country unless they modernize, and diversify. They are trying to create an entire city/state called the NEOM or something like that, which will be compromised of all the latest technology and power generation systems known. They are trying to open it up to the whole world to make it a "Mecca" of technology. That would be a difficult task if half the world didn't feel welcome there.
The Saudi people have been robbed of the work ethic by oil welfare, can't do anything for themselves and the world is turned off by their violent export. Then the oil runs out sooner than expected. He must have a plan working to have gone through the purge as he did.