Directly paying everyone living/working nearby to get them to accept cut and cover construction? Wouldn’t that cost even more then building it deep underground, after all the legal fees and court challenges, once it’s said and done?
Lot of money to go around, I'd argue its more political will than cost.
Don't forget theres years of legal fees & court challenges even with deep tunneling!
There's no simple reason - basically everything that can cost more, does.
A lot of it is that every last bit of expertise is outsourced.. not just physical labor and renting equipment but even the project planning, management and oversight. You'd think given decades of capital programs lined up, the state would want to have their own planning/management/oversight staff so that interests are more aligned.
You can't pay yet another vendor to care about & enforce cost discipline upon all the other vendors you are paying..
You also can't discount antiquated union work rules & strong lobbying. NYC transit work sites are more heavily overstaffed compared even to the equivalent Paris transit project. "Our unions have more power than in France" is a pretty high bar. From having 3x the staffing on the Tunnel Boring Machine to minimum required union machine oilers on-site based on the level of hand oiling that 1970s equipment needed (far more).
It's like if IT's staffing / roles were frozen in time from the 1970s and we still paid someone to sort punchcards.
So only what, about 30x as much as Madrid spent?