The slow moving disaster that is the Colorado River is a particularly American disaster. The manifest destiny mindset coming to an abrupt end. In the book Cadillac Desert Marc Reisner asserts that this could be the albatross that contributes to the downfall of the US. The more I learn, the more I’m inclined to believe him.
It's very frustrating, because it's clearly a problem, and also clearly a solvable problem. Yet, actual action moves at geological timescales (in this case, quite literally).
It reminds me of the extinction of the passenger pigeon. Not only was it's population hunted to collapse, people went out of their way to make sure they rooted out the last nesting pairs and fully exterminated it.
As to exactly why, who knows? What could a handful of birds have been worth?
The bill has come due for us to build more infrastructure, not pretend like we're going to stop growth and catastrophically damage the economy in the process.
Glen Canyon was built in the 1960s. Because the infrastructure enabled so much growth, demand is outpacing supply.
Arizona is trying to build a desalination plant in the Sea of Cortez to solve the Colorado River problem and the environmentalists immediately came out of the woodwork to complain about it. The mass media then, in a coordinated fashion, pushed FUD about how desalination is bad for the climate because it will require energy (Arizona is a leader in carbon-free nuclear and solar energy), will be too expensive, it'll destroy habitats, etc. At some point you start to realize the sentiment is entirely political and has little to do with finding practical solutions.