2 reasons nobody has (surprisingly) mentioned yet: - Trains: the Acela is established and successful, already taking about half of the passengers on the Easter

2 reasons nobody has (surprisingly) mentioned yet: - Trains: the Acela is established and successful, already taking about half of the passengers on the Eastern corridor. - Right of way: (to borrow one of your sentences) the population density of thses places [East Coast] drives up the cost of the infrastructure. Another factor might be that the design is better optimized for 400 miles than for 200. The capsule acceleration phase is necessarily long and energy-intensive, so you want to optimize that over longer distances. It's the same reason that high-speed trains don't have stops every 20 miles.