That sounds fine and dandy, but they don't grow food there. That's going to be a much bigger problem than whether or not people can tolerate being indoors all day.
Water rights between states and between nations are going to lead to war and mass migration.
https://extension.arizona.edu/arizona-citrus-resources
https://www.arizonabeef.org/the-beef-story/cattle-in-arizona
https://www.cooperranchlife.com/contact
https://azgrassraisedbeef.com/shipping/
Of course, the urban landscape as it is now, used to be dominated by farmland, and so it isn't what it used to, but if you meant to write "they can't grow food there" that also another lie, because there is plenty of food that grows quite well here. In fact, several of my friends love to share the produce from the trees in their yards and their backyard gardens.
Not much happens in the summer, that's true, but since all SW ag is irrigated, a lot is grown during the rest of the year.
Now I can't stand Sonoran Desert summers, not possible to be outside comfortably, but a lot of people really like the rest of the year there.