Why do you think the Saudis are pouring so much resources into these experimental line cities? Even they know that the system they helped create and benefited from is unsustainable, and building a self contained city in the middle of the desert is them testing the hypothesis of, can you build a habitable zone for humans in the worst case scenario of environments?
It also ties into why there are so many billionaires who are obsessed in advancing space travel as quickly as possible. Even they are starting to get nervous about the Earth they have created and will have to live in.