I have been to a few rallies/vigils/marches lately and all incidences of violence that I have witnessed either in person or through media has been instigated by the police. As far as I know,every documented case where a formerly peaceful crowd turns into chaos has been started with police shooting pepperspray, teargas, or whatever into the crowd.
I find it really hard to not come to the conclusion that the police is desperately trying to set a narrative to justify a history of violence by escalating more violence, but please, someone, restore my faith.
This has been a long time coming, too. In the last few years, many police departments around the country have thrown their hands up and publicly stated they won't be bothering with most property crimes. The way they see it, the only crimes worth their time involve people not committing real crimes at all or crimes involving guns or knives. Anyone who doesn't get why people don't trust the police has been living under a rock. This goes beyond just racism.
They want the story to be about rioters so they're letting them riot. It's a way to shift the public opinion (same way some cops have been seen breaking car and store windows).
Not showing up can be a tactical decision: you don't have to generate more bad press and more cries about police brutality and you also don't need to quasi-officially hand over the area to the looters.
The state's power isn't real as in "we can crush you", it rests only in everybody's fear of the state being able to crush them. If there's a chance that the state has to back down, not seeking the confrontation sounds like a smart choice to me, even if it comes at the price of a day or two of looting.
Your argument can't possibly be "Because they didn't want to escalate" or "They didn't want people to think they're violent" when they did escalate and were violent elsewhere.
I am in full agreement that it was tactical - it allows them to punish a neighborhood and to shift the story.