The cops are probably thinking that, without the news crews there to give the rioters their forum, the rioters would be back to their usual evening activities by now.
The KKK used to hold a march in Pulaski, TN, the birthplace of the KKK, every MLK birthday. When the news crews stopped coming, the marches either ended or have become so small as to be insignificant. I haven’t heard about another march in years.