Costs are a major part of the problem. US rail construction costs are by far the most expensive in the world [1]. Other countries are able to build rail at costs in the $100-250 million per km range (even in dense cities). The East Side access project in NYC has costs around $4 billion per km. Los Angeles has much better costs in the $400-500 million per km range [2]. Its hard to imagine the US will be able to build much transit at those costs.
From 2012[3]: "When asked by transit blogger Benjamin Kabak about its high construction costs, Michael Horodniceanu, president of the New York City Metropolitan Transportation Authority’s capital construction division, gave a two-word answer: “work rules.” Citing the example of the city’s revered sandhogs, he said the MTA employs 25 for tunnel-boring machine work that Spain does with nine."
There's problems on the operations side too. The same agency that is building that East Side Access (LIRR) still does fare collection by sending well compensated employees walking up and down every train to punch paper tickets twice per ride.
I don't know if it's an urban legend or not, but I've been told that one of those conductors punching tickets on every train is technically designated and paid as a "fireman" i.e. person responsible for shoveling coal into a boiler because the collective bargaining agreement forbids them from eliminating the position.
From 2012[3]: "When asked by transit blogger Benjamin Kabak about its high construction costs, Michael Horodniceanu, president of the New York City Metropolitan Transportation Authority’s capital construction division, gave a two-word answer: “work rules.” Citing the example of the city’s revered sandhogs, he said the MTA employs 25 for tunnel-boring machine work that Spain does with nine."
[1] https://pedestrianobservations.wordpress.com/2011/05/16/us-r... [2] https://pedestrianobservations.wordpress.com/category/transp... [3] http://www.bloombergview.com/articles/2012-08-27/labor-rules...