US rail infrastructure is also more expensive just as a simply supply and demand problem -- we have very, very little supply compared to in Europe. We've fallen so far behind in the technology that most major projects involve bringing in contractors from Italy, Germany, and France to do the work. We even import most of our new rolling stock (and the Class 1s nearly never buy new rolling stock anyway, if they can help it). We're buying and building so little rail that we've lost the capacity to do it well ourselves and so have to import it at a premium.
Plus the US federal system -- and its general philosophy with e.g., city departments competing with each other for budget -- just makes infrastructure projects super expensive in general.
We need to start investing in it again to see the cost drop but people refuse to invest in it because the cost is so high. That might just be starting to change with Cali HSR, Brightline, the mid-Texas HSR project, Amtrak ConnectUS, etc., but we'll see.