> a pretty hostile terrain - Italy has lots of mountains, hills, rivers

So does U.S., a lot more in fact. The length of Italy north to south is 1,320km, the distance from San Francisco to Chicago is 3,220Km and that's only 2/3rds of the east-west distance of the continental U.S. And there are two major mountain ranges to cross on that trip, and huge stretches with almost no population. (How many deserts to cross does Italy have?)

Trains need crews, the crews need to work in shifts, the crews need to be available along the way, even in Nowhere, Nevada. That causes delays and restricts schedules.