In the US, I can get my family from Boston to DC and back on the high speed train for the cost of... a used car. A decent used car at that, which is why we drive instead of take the train.

In China, by contrast, trains are getting faster and faster-- What used to take nearly 40 hours (the Shanghai to Beijing run in the early 1960s) is now down to about eight hours for the fast nonstop, and train tickets, especially on the slightly slower trains, are very reasonably priced. Chinese trains move, literally, hundreds of millions of people on a routine basis. And fast. If you wanted to go to Tianjin, which I don't, the trip takes about half an hour to go 120km, with trains departing every ten to fifteen minutes. Tickets are about $8 and about $9 for first class.

Trains in this country need to speed up and get a lot cheaper before people will consider them a viable alternative to flying or driving. It's a matter of public policy: if there is a greater social benefit to people using trains, then the government should support and subsidize train usage. If there is not such a benefit, then left to market forces, passenger train service will remain a minor piece of the transportation pie.

I thought perhaps you were engaging in a bit of hyperbole, but a quick jaunt over to the Amtrak website shows that for the Acela, there's no such thing as a child's fare or an economy seat. Taking my family of four from Boston to DC and back priced out to $1800.

Found a nice 2001 Daewoo Leganza on Craigslist for $1500. Four doors, leather seats, and you can discard it after the trip.

But the Acela is consistently sold out. Shouldn't Amtrak price the tickets to the market?

I think perhaps that China is a bad example since the cost of living is so different.

Japan might be a better comparison. I used to live just outside of Nagoya city.
To get to Tokyo :

by car - 5 to 7 hours and ~10,000 yen ($95) each with including tolls and gas.

by shinkansen - 1.5 hours and 10,500 yen ($100) per ticket.

So for a person going solo, of course you will take the Shinkansen. But for a family? Unless you are in a hurry, you take your car.

And the Tokaido Shinkansen (between Osaka and Tokyo) is very profitable, and is running at capacity. JR Central subsidies its regular non-profitable local trains with the massive profits it gets from its shinkansen line.