Someone said this earlier, but it keeps being missed. NYC already spends $8 billion on health care for the uninsured, so that explains why this additional expenditure is so small. See:
New York City already provides health care to the uninsured and the undocumented through its hospital system, a roughly $8 billion behemoth whose history of service to the poor, regardless of an ability to pay, can be traced to the founding of Bellevue Hospital in the 18th century. A person without medical insurance has long been able to go to a city emergency room and get care, free of charge, or to seek a primary-care physician.
Source:
https://www.nytimes.com/2019/01/08/nyregion/de-blasio-health-care-plan.html