1. Privatization has been an absolute disaster for the rail industry. Privatization has simply become a way to privatize profits and socialize losses. The advent of Precision Scheduled Railroading ("PSR") [1]. It not only decreases safety but leads to massive delays for passenger trains who can't pass the longer trains that PSR results in;
2. A car-centric culture that originated after WW2 that ultimately came from excluding poor people, particularly people of color. There is a strong cultural bias against any form of public transportation because many view it as raising taxes even though road infrastructure is heavily subsidized; and
3. Further to (2), there are some billionaires who capitalize on this attitude and fan the flames by fighting against any form of public transportation and passenger rail (eg [2][3]); and
4. The US suffered from a first mover advantage. From the mid-19th century, the US built a massive aamount of rail infrastructure. This was designed for far slower trains. You can't just put high speed trains on the same track. China in comparison didn't have that problem; and
5. The pre-eminence of private property in the US makes building anything like this difficult and expensive. Yes, there's eminent domain but local and county authorities can hold things up for years. If you look into the California HIgh Speed Rail project, you see a lot of concessions have been made with the route and stations in relatively low population centers just to get planning permission, which increases the route length and the LA and SF travel time.
[1]: https://www.npr.org/2023/03/23/1165699563/how-precision-sche...
[2]: https://www.theguardian.com/us-news/2019/aug/26/koch-activis...
[3]: https://jalopnik.com/did-musk-propose-hyperloop-to-stop-cali...