[jcranmer]

Several reasons:

* Airplanes travel about twice as fast as top-speed HSR. By 5 hours, even assuming generous airplane penalties, there's no speed advantage to HSR.

* For business travel, you've already lost the entire working day at that timepoint, so downtown-to-downtown isn't as much of an advantage anymore.

* You start to have to have nasty scheduling times for intermediate stops. Having to disembark at 3:00 AM is not going to be conducive to ridership.

* Sleeping cars and full-service dining start to become necessary around that point in time, and that's really going to eat into your operating costs.

I drove the number of 5 hours largely on the meal concern, but it does seem that most planning exercises tend to profitability wall closer to the 3 hour mark.