You’ll never take HSR from NYC to LAX but Chicago or Atlanta from NYC is roughly the same distance as Paris to Berlin, and there’s a bunch of cities on the way as well.
Maybe in Germany, but France has barely populated areas and yet we have one the biggest high-speed rail network on the planet. In fact, the fact that France is the biggest European country after Russia is probably the main reason high speed rails was invested on back in the 70s: the bigger your country the more you need high speed rail.
High speed rail is not going to do a lot of good in South Dakota, but we can serve most Americans with some type of decent rail without contorting ourselves. And the bar is on the floor since a lot of Amtrak is not even a single round trip seven days a week.
Even in a mostly suburban metropolitan area, most people are still quite a ways from the main airport, which is usually on the extreme of one side of a metropolitan area. You can have multiple train stations per city because of their much lower footprint and nuisance level, and generally speaking most of the time savings in rail vs air is access time to the station/airport. (Truly high speed services can just skip the suburban stations if there truly is demand for this, but generally speaking the time for an additional station is measured in single-digit minutes.)
Ironically car dependent cities like LA were built out as streetcar suburbs so they’re not really all that different to London’s ‘metroland’ suburbs built out around tube lines. The big difference is the job centres are far more distributed. When offices as well as homes are widely distributed public transport becomes very tricky.