The FRA puts out a lot of stupid safety regulations that don't apply in Europe and which make high speed rail much more difficult. US trains have to be built like tanks in the theory that this will help them survive collisions with freight trains. The fast accelerating French trains can't be used on US rail without special permits.

https://bikeeastbay.org/rail/fra.html

And for various reasons rail construction in the US costs about 5 times as much as it does in France. And because it costs more we do less of it. The figures below are for subways but I believe long distance rail sees the same effect.

https://pedestrianobservations.wordpress.com/2011/05/16/us-r...