High speed rail is also a bit of a red herring. In dense areas you’re not actually going to go fast! “Normal” trains would work fine and be helpful.
TGV and Shinkansen go really far! But what makes people in France or Japan take the train a lot is much more around local trains that are just going at normal speeds.
I think the counterpoint in the US is that most cities are very far apart and there is practically nothing in between. Obviously places like the northeast corridor or the Bay Area are much more dense. But even a route from SF->Seattle is mostly traveling through non-dense areas. That gets even better across the west and Midwest
Wires than that. Most people live on the border of the cities and the nothing. Suburbs are practically designed to make mass transit expensive and slow.
TGV and Shinkansen go really far! But what makes people in France or Japan take the train a lot is much more around local trains that are just going at normal speeds.