> Rail systems work in Europe because densities are extremely high.
Rail systems work in Europe because European cities have decent local transit/walkability. Rail systems are challenging in the US because the US invested heavily in destroying local transit and walkability for a mixture of reasons (auto industry influence, deliberate attempts at de facto racial segregation, especially in the wake of pressures against de jure segregation, and some other reasons), so once you get somewhere by rail you can’t get anywhere else, unless the train station wastes a whole lot of space – and airports already do, but its less of a burden for them because airports need to be pretty sprawling to start with — having giant parking lots for round trip passengers and rental cars and for access to serve as giant road transport (bus, taxi, rideshare) hubs.
Which is why you can’t just build long-range passenger rail in the US, you have to also build or significantly upgrade local transit networks at the termini and intermediate stops and also deal with the local development patterns in all those places (you don’t have to do it all at once, but if you don’t, you have to accept that you aren’t getting all the benefits until you do.)
And you are going to be fought the whole way by forces that recognize the connections and oppose any part of it, for any of the reasons the status quo exists as it does.