There isn't enough demand for train travel to allow Amtrack to make it as a private corporation.
There is not enough demand for trains with average speeds of 40 miles per hour between major cities. Intercity trains of the past at least ran at average speeds of 60 mph, sometimes faster; on the so-called “Northeast Corridor”, they run at average speeds of 70 to 82 mph, but still could go faster with the right technology.
Before Amtrak was created, there was more than twice the number of trains running intercity, BTW. Regulations and taxation ate into private railroads’ bottom lines, not permitting them to compete with other modes—and this is still the case today.