Eh, the problem is the city is now incredibly built up. New stations have to be built even deeper than before to avoid hitting building foundations and utilities.
Those earlier companies had the ability to do mostly what they wanted, including building incredibly piss-poor stations that can't withstand the test of time, while making it near impossible to renovate the station because they cut every corner possible and included no bypass tracks.
They were also able to pay peanuts to send humans into harrowing situations to get the tunnels and tracks and etc. made, collapses or flooding or other injury-inducing hells be damned.
America does build infrastructure painfully slowly and bureaucratically, but I don't think we're ever getting the early-1900s esque speed of building back at a price public entities will pay (or a price private entities could ever realisticlaly recoup). Enough rules have been written in blood to ensure that.
Instead, the system has decayed.
A demonstration of how competition fuels progress in infrastructure.