Worth noting that Paris has famously powerful unions and yet still manages to build transit projects for much less than New York City.
It's more an image than a reality. And in the case of construction workers, it's completely false.
When the basic of budgeting, whether public or private, is "use it or lose it", there's no incentive to lower costs - because if you lower costs now, then next year you won't get funds to do something useful.
You can also go the other way around, where you give a bonus based on amount of unspent budget... Which quickly results in all spending cut where possible by the person who would get said bonus, regardless of whether it damages the goal of the organisation or not, and with no care that long-term effect might be higher spending than not (for example due to half-assing vehicle maintenance).
... And yet, things we buy from private companies tend to get cheaper and better over time. It's weird, isn't it? I think the big difference here is that private companies are not immortal monopolies, but government agencies are. Sears was the Amazon of its day, and gradually became less impressive -- but we weren't screwed, because now Amazon is the Amazon of its day, and in time we'll find out what upstages Amazon. In contrast, the government of New York used to be unusually good at building subways -- but now it can barely maintain what it already has, and people living in NYC are just stuck with it, because there's no realistic mechanism for the department in question to be replaced with a more competent one.
I'm increasingly convinced that solving this category of problem is one of the most important unsolved political questions, and it's tragically under-explored.
Not necessarily. Bruges lost its dominant economic place in the Low Countries because they failed to invest in maintenance and the canal to Zeebrugge silted over. Much the same happened in Saint Louis and explains how Chicago became the capital of the Midwest despite a couple hundred years' late start.
I doubt New York will go the way of Detroit, but that is an object lesson of what happens when cities don't stay on top of things.
There are plenty of government projects done on time and at reasonable cost. Nobody here knows about them because you will never find them in the trendy major metros and upper class suburbs in which the occupants of HN live. Those places have money to burn so they burn it. Rust belt cities and Nowhereville rural towns and other places strapped for cash generally get their moneys worth because people the world over generally do their jobs and for the bureaucrats calling the shots in those places spending the minimum amount of scant resources to get something done is just part of the job. People shit on these cities for their crap roads, their run down school buildings and generally not being up to the kind of standards that a bunch of upper middle class people expect but you know what, their roads and their schools work just fine.