An example to the UAE citizens that their government will protect them. Sense of citizenship is worth $20B. Plus, it's not that UAE actually lost this money. Neither did France. They may lose/delay $20B in revenue.
UAE is full of very wealthy expat Russians who have UAE citizenship. If UAE does not protect them, they might go elsewhere and take their money (which probably is at least $300B) with them.
UAE would not protect an ordinary citizen like this.