Part of the issue is there's no good model to build transit fast short of privatization, and that even in nyc was dependent on temporary economic conditions that turned sour and bankrupted every operator. There's the japan model of financing this transit through ongoing real estate ownership vs just selling lots like old private american transit, but even then a lot of their build out was decades ago when labor and materials and land value was much cheaper, especially compared to present day american cities. Its something the federal government really ought to just spearhead like the interstate highway project, but with the current environment politically even if that did somehow have bipartisan support, there would be a ton of waste from corruption as the vultures smell out all the available flesh and probably help lawmakers write the proposals for these projects in such a way to favor themselves.