When I saw this posted elsewhere, some commenters pointed out that this was not an effort to "catch" skaters in the net, but to divert them off of Broadway, and also possibly toward cops off to the right waiting to arrest them. Notice how the only person they actually stop in the video is someone who doesn't turn right, and instead walks around.
In terms of the police disrupting traffic here, notice how they move back and forth between streets; they're only blocking streets while lights are red. The skaters in this race appear to have universally ignored traffic laws, especially lights, and so the only people this should have really disrupted were the skaters. Of course, as seen in the video, the solution appeared to have been to skate on in the middle of the other side, against traffic, and still run red lights.
It's honestly a bit odd why so many people seem to support this race; it's dangerous to the skaters and others, and disruptive, and it feels like these are actually some of the major draws. From videos of some of the participants, it feels like the general view was that traffic laws, police, cars, and right of way could be entirely ignored, and pedestrians could be run down with impunity as long as the skater shouted "I'm not stopping!" first.