If islamists anywhere in the world get into a war for all the marbles with a nuclear power, Mecca and Medina are logical targets.
If the Allah described in the Koran exists, Mecca and Medina are under divine protection by an omnipotent god.
If Mecca and Medina can be obliterated, than any Allah that exists is not the omnipotent god described in the Koran and the Hadith. Destroying them would be a knockout moral blow.
The Saudis have to see the precariousness of their situation.
Tha Saudis have more to worry about than the kaabaa being blown to smithereens, which would shatter islam. Every one of the house of Saud have genetic markers making it easy to target the group with an engineered plague.
Leaving no Sauds alive anywhere in the world.