Recently, Technology Connections on YouTube had an interesting theory¹: Long-range trains will never be popular in the USA, since people there have so little vacation time. It’s not reasonable to blow a few days (in total) on just train travel if your entire vacation is a single week. Other places don’t have this problem, so trains are more popular.
1) https://www.youtube.com/watch?v=VDV1R1j1n5I