[M T]

 How the hell do the people of the country allow this profligate spending on such silliness? How do the economics even work?

Wikipedia classes Saudi Arabia as an absolute monarchy, which it defines as

Absolute monarchy is a form of monarchy in which the monarch rules in their own right or power. In an absolute monarchy, the king or queen is by no means limited and has absolute power, though a limited constitution may exist in some countries

So, your question is rather meaningless.

[M T]

 How the hell do the people of the country allow this profligate spending on such silliness? How do the economics even work?

Wikipedia classes Saudi Arabia as an absolute monarchy, which it defines as

Absolute monarchy is a form of monarchy in which the monarch rules in their own right or power. In an absolute monarchy, the king or queen is by no means limited and has absolute power, though a limited constitution may exist in some countries

So, your question is rather meaningless.