[bryanlarsen]

For many people, the bus/train is the better experience. It takes less time during rush hour, and you can read/nap/work during the ride. I imagine that private plane slots at an airport have a fairly limited availability, so if they become popular you'll have congestion issues too.

[netnichols]

Indeed. In many parts of the world the normal intercity bus ride is a quite pleasurable experience, significantly better in many ways than flying a budget (or pretty much any) airline.