This is more insightful than you know.

MBS was a chubby bookish kid playing Age of Empires out in the hinterlands when he realized there was an opportunity so he arranged a trail of dead between him and the throne. He was something like thirteenth in line, and there were something like 400 other princelings at his rank, and now he's the undisputed heavyweight champion of the world.

So the first thing to take from that is that MBS is an autodidact. What moves he's made he learned from video games. The second thing to take from that is the autodidact outmaneuvered the fucking CIA.

The other elephant in the room is that our petroleum economy cannot last forever, and MBS is 39. He likely has exquisite insight into the state of Saudi oil production and by extension and espionage, the oil production of much of the rest of the Arabian peninsula. The task, then, is to give the rest of the world a reason to care about the Arabian peninsula when the oil is gone. What's the quote?

"If you owe the bank $100 that's your problem. If you owe the bank $100 million, that's the bank's problem."

- J. Paul Getty

The way to look at petrostate megaprojects is as lures for foreign investment. There's no reason for Las Vegas to exist, and yet there it is. Las Vegas will exist in a hundred years. So will Baku. Dubai didn't exist thirty years ago - will it exist thirty years from now? Depends on how much foreign investment can be attracted. And if you're MBS, you can turn on the "authoritarianism" and "slavery" cheat codes. And it's hard to argue with a guy who (A) can disappear you (B) is where he is because he beat the experts.

The fundamental model for life on the Arabian Peninsula has been "coastal or else." There's only so much coast. The techbros are all about mars colonies and shit; an Arabian Desert colony is fuckin' easy mode compared to that. The WHOLE point is to get enough crazy-ass early buy-in to push the project over into "it's cheaper to complete it than abandon it" at which point you're a visionary.

From an urban planning standpoint it's a dumb fucking idea. Anyone disputing that is either clueless or cloaking their agenda. From a Civ VI wonder-building standpoint it increases your prestige and you can always suppress your citizens or start a war to buy yourself some time and everyone else is an NPC anyway.