The obvious reason is goods and equipment movement. There are places that strike a much better balance than NYC though...

How do you get all the food in? Manhattan is an island. Without constant food deliveries by truck it will die. This food is delivered to countless restaurants and grocery stores, not to some central warehouse, so delivery by train doesn't work.

While I wasn’t claiming it would work, that example is easily solved around the world already by allowing vehicles into pedestrian zones overnight.