I'd imagine the police are better able, and more used to dealing with this kind of low level disorder.
I was also reading something last week about the use of more aggressive anti-riot tactics in Europe, and the argument was that they can be counterproductive. The police response is almost certainly to prioritise people not getting hurt, and when it's small numbers of idiots, who can be mostly contained, and then taken to court the next day, they are probably happy.
A more confrontational response could inflame things - a few major injuries on the rioters side, could bring out many more, and a more pro-active approach might draw in more people from the 'shouting but watching' side, to the actively rioting.
The police have got to go back and work in these areas the day after a riot, and it doesn't make sense for the state (whether it's the police or the army), to be seen as the enemy.