This might sound like a cop-out answer, but I think the answer is "nobody knows".
So-called "cost-disease" spans infrastructure, education (public & private!) and medicine (again, public and private). All of these things cost 10x what they used to and 10x what they cost in other countries.
NYT tries to answer the question for NYC (but then why is cost disease a thing in other cities with different contractor/union/transit authority interactions?)[0]
Alex Tabarrok says it's growth in demand and slowdown in productivity growth (but then why is this a US only phenomenon? Does it really "jive" that infrastructure costs 10x what it used to because of "increased demand and slowdown in productivity?" I don't think it passes the smell test) [1]
So-called "cost-disease" spans infrastructure, education (public & private!) and medicine (again, public and private). All of these things cost 10x what they used to and 10x what they cost in other countries.
There are a few exposés and studies that try to explain the issue but IMHO none of them are satisfactory:
NYT tries to answer the question for NYC (but then why is cost disease a thing in other cities with different contractor/union/transit authority interactions?)[0]
Alex Tabarrok says it's growth in demand and slowdown in productivity growth (but then why is this a US only phenomenon? Does it really "jive" that infrastructure costs 10x what it used to because of "increased demand and slowdown in productivity?" I don't think it passes the smell test) [1]
Slatestar codex says "beats me" [2] and [3]
[0]:https://www.nytimes.com/2017/12/28/nyregion/new-york-subway-...
[1]: https://www.mercatus.org/system/files/helland-tabarrok_why-a...
[3]:https://slatestarcodex.com/2017/02/09/considerations-on-cost...
[4]: https://slatestarcodex.com/2017/02/17/highlights-from-the-co...