It was mostly due to work by Giuliani’s predecessor, David Dinkins. I wrote a longer comment about it.
The ‘broken windows’ theory was really an excuse to put black and brown people in jail for minor crimes. People still hop the turnstiles, but that’s not the real source of crime.
Look at the overall economics of the period, once Reagan was gone and the people in NYC could start getting jobs again… What’s attractive about being a criminal? It’s hard, and there’s always the chance someone’s got a dagger or pistol on them.