Budget, Federal Money LOTS of Federal Money, and a willingness to spend it.
They also have Agusta 119's you know.....N318PD being one of them.
Last time I checked that was a single engine aircraft.
At one time they had eight of them, two 412's as well.
Why do Bell's and MD's and even R-44's get used by the vast majority of other PD's do you think?
http://www.oocities.org/floyd_bennett_field/nypd.html