We are a very vast country. Eurostar works great but Italy is the size of Arizona. But it also has major cities contributing to demand like Rome, Florence, Venice, Milan, etc. That is a lot more like the NE corridor route, dense populations in a relatively small area (DC, Philly, NYC, Boston)
I do think we can expand rail in states like California and Florida. I think large populations in small areas make rail ideal. That’s why it seems rail works great as a metro system.
But not on a route like NYC to SF. The distance and spread out population just makes it harder.
But I’m no transportation expert. I do think it’s our geography and density that make it inefficient here.