Congestion is worse. Rush hour in Chicago now covers eight hours per day. That's pretty expensive to move your body in your car 15,000 miles a year. Aviation's ability to expand is on a par with the problem of legroom in its passenger seats. The cabin can be reconfigured to add an inch or two, but that's about all.
Load factors are at record levels.
Passengers are furious over delays and overcrowding. With Herculean effort we are able to add an airport like Denver International once every 20 years. Alternatives such as VTOL aircraft have stalled out. Airport managers' visions now are limited to their existing property boundaries. This approach simply is not sustainable.