> HSR is more of a more efficient airplane - spacious & can walk around & get a drink.
Much as I love HSR and curse its absence when in the USA the economics are not quite as clear. Air routes are more flexible than rail routes.
Of course that flexibility isn't necessarily desired by all; the stations on a rail network provide hysteresis which can keep otherwise unprofitable cities alive and even vibrant. New York beat out Boston because the Hudson was more navigable than the Charles, Boston Harbor's benefits notwithstanding. Chicago grew because it was at a confluence (literally!) of cheap transshipment points near farmland. Both cities do well even though their original reasons for existing are lost (neither are major freight hubs but have a lot of other transit links).
And rail, even underground rail, can be abandoned.
In fact airports can be / often are built far from urban areas where land is cheaper and space is available not just for the runways and terminals but parking, cargo etc. While you want rail terminals to be in densely connected locations which are more expensive and more difficult to network to.
But my point is that you can relatively easily fly from one airport to many others. For example, the under-construction California HSR goes from LA through Bakersfield in the Central Valley up to SF and then Sacramento. If Fresno in the Central Valley grew, you could expand its commuter airport and then it would be directly linked by air to Burbank, San Jose, San Franciso etc as well as points outside the state. While the cost of adding an HSR terminal in Fresno could be large, especially if the rail doesn't run nearby (as it happens a terminal appears to be planned in Fresno, but the point remains).
I'm still a big supporter of HSR but I recognize the trade offs.
Much as I love HSR and curse its absence when in the USA the economics are not quite as clear. Air routes are more flexible than rail routes.
Of course that flexibility isn't necessarily desired by all; the stations on a rail network provide hysteresis which can keep otherwise unprofitable cities alive and even vibrant. New York beat out Boston because the Hudson was more navigable than the Charles, Boston Harbor's benefits notwithstanding. Chicago grew because it was at a confluence (literally!) of cheap transshipment points near farmland. Both cities do well even though their original reasons for existing are lost (neither are major freight hubs but have a lot of other transit links).
And rail, even underground rail, can be abandoned.