If this isn’t shut down quickly, I predict we see a national movement like this by Juneteenth.
So the police aren't going to storm the barricades -- they figure they won't have to.
The police let the anarchists do whatever they want, within certain constraints (no injuring people, constrained to certain neighborhoods), and the anarchists only do it on that day of the year. Sometimes there are conflicts between the police and the rioters, but it never escalates to huge conflicts any more.
It’s a display of mutual respect for authority, and it allows the radical groups to blow off some steam, while campaigning for progress.
I know this idea makes no sense to law and order -type people, but it’s an ancient human idea to ritualize and sanctify the behaviors you want to discourage or control.