Ego instead of profit
I doubt very much the numbers justify the design of this building. To grossly over simplify, land has to be so costly that it's more economical to build 157 floors up than to have a building twice the footprint & 79 floors tall, 3X & 53 floors, etc. Kingdom City is going up near the Red Sea, not on an island in it. At some point, people & companies decide they don't need to be in the tallest building in the world when they can save a lot on rent & be in another building just as nice nearby.