An enduring mystery with profound consequences for the sad state and sluggish pace of building public infrastructure in America has been resolved:
The reason it costs so much to build new public works projects is that states outsource their management to armies of consultants, rather than hiring and retaining the staff required for governments themselves to do it.
https://slate.com/business/2023/02/subway-costs-us-europe-public-transit-funds.html
@mimsical