We do need density at the end of that rail line - dense towns connected to a dense metropolitan hub via a fast rail line. For example Ann Arbor to Detroit, Davis to Sacramento (neither of which have fast rail lines to connect them).

What we've built instead for more than half a century is continuous radiating sprawl.

There is no way the tax base of the boonies can support the initial and operating costs of a rail line. Therefore it is not an option, and why you do not see it anywhere.

Even suburbs cannot afford all of their ongoing infrastructure obligations, and why you see many dilapidated areas.

This is all becoming apparent now because birthrates have plummeted hence what used to be masked by economic growth due to sheer population growth no longer has the ability to be papered over with increased tax collections due to increased population.