There are several reasons why high-speed rail hasn't taken off in America. I think in certain, specific areas it can be successful (northeast corridor has some, texas metro connect) but this pie in the sky idea that all of America should be like Europe and have high speed commuter rail is just not feasible.
1. Geography is a major factor considering the United States is massive in comparison to Europe.
2. Majority of our major cities were built with cars in mind, and we have become a car centric nation with the build out of our interstate system. around a century ago the major players in the car industry (ford, firestone etc) agreed to push cars over trains.
3. As a nation we prioritize freight rail over passenger rail.
4. Self driving cars are already coming onto the scene and they will just get better and better. It would be a massive waste of money to go and build out a passenger rail infrastructure when in the next couple of decades, the majority will have fully autonomous self-driving vehicles.
The time for America to have fully functioning passenger rail line everywhere was over 100 years ago. The time has passed and we opted for cars and planes.