The whole country is moving in the opposite direction, of allowing ordinary citizens to carry concealed, and the courts are backing that view up pretty well so far. So, why waste millions and millions of taxpayer dollars on a machine that will detect something that is sure to be completely legal in NYC within a few years?
That's an excellent point.
Under the present conditions in New York City, one might expect that most people concealing a weapon are "criminals". When this is no longer true, then the invasion of privacy which would occur by revealing what is inside the pants of a law-abiding citizen would become even more stark. No Warrant, No Zap.