I don't think LAPD can afford to live in that part of L.A. Unless they went back to drug dealing like the did in the 80's/90's. Ooooooh You're talking about that other gang.

Once you're incapacitated by the blue lights, there's not much you can do I guess. And gangs don't have access to heavy weaponry like the military does. Plus, the fact that the aliens regenerate and come at you time and time again doesn't help the situation.