Hip Hop in NYC was a deejay-centered, youth-driven, music party culture pretty much up until
the mid to late 80s.
The extreme violence associated with the decade of crack trade/crack culture from '85-'95, destroyed the
park/community center/dining hall/skating rink independent party aspect of previous the NYC b-boy scene.
Shootouts at The Rooftop, Union Square, Latin Quarters and Encore's did the same thing to the club scene.
As the party aspect died, the rapper recordings-based industry rose, minimizing the deejay and turntables scene.
Meanwhile r&b, club and house continued to live at Bentley's, The Silver Shadow and Zanzibar's. Dancehall was also pumping from Brooklyn throughout the city late 80s/early 90s with Shelly Thunder, Tiger, Super Cat, etc.
When Yo MTV, The Source, and Hot 97 enter the industry as white-run tastemakers, all the nuances of NYC youth music variety were strained out, and have been homogenized ever since.