If a train line is not profitable, its not used

Peak car/capitalist brain. You gonna hold roads to the same standard?

How do you feel about rural roads? Should we not build them unless we can make them profitable?

I think you have that backward, even accepting the idea that profitability is an important metric. If a rail line is not used it is not profitable.

they should be built/deployed at a capacity as its needed in order of minimizing waste

Building at capacity might not be the most efficient solution. First, towns grow. Second, China keeps costs down by standardisation (the Chinese HSR system has, if I remember correctly, 3 models of trains and two standards of track). And third, China is vulnerable to earthquakes and floods. So having alternative routes is useful.

1. Comprehensive transportation systems have huge indirect benefits for a society. While they lose money in direct fees, they support large economic improvements. For any transportation systems. Cars are good for widely dispersed populations, aircraft are good for long distances, trains are good for large groups of people and medium distances. Why can’t we invest in the right transportation for each use, give people access to the best choice? Instead we limit our choices, limit our options, even when they’re not the right choice
2. Adding gas taxes and tolls together, typically covers less than half a highways cost, and most roads don’t have tolls. Roads are not profitable or taxes are not sufficiently high.

China is state capitalist…

Sources: https://en.wikipedia.org/wiki/China_Railway_High-speed#Ridership

If your government isn't planning decades into the future, it can't meet any needs at all. It takes that long to build things to address large issues. There's a lead time. If you don't start planning and building well before there is a need, you'll always be late and will be seen as useless.

I guess that does explain the American government actually.