Where did you come up with the assertion that they did not do that also?
The officer writing Wong a ticket shouted for backup and witnesses said it appeared almost instantly (according to earlier articles.
Now, how do you suppose that was able to happen?
At 80 cops per square mile, NYC is crawling with cops. The way it works is they typically hang out in the same areas instead of spreading out. I've been to plenty of run-down areas where the cop presence is nugatory. Weirdly enough, the highly-patrolled areas tend to be upscale areas like 96th St. That's why I thought stop-and-frisk was a wonderful thing - it provided poor areas with a police presence. Now that it's been ruled illegal, the cops appear to be hogging all the low-crime pedestrian areas again.