That's because to the BLM crowd, black life is thuggin' and druggin', lootin' and shootin', and they want to retain that separatist and supremacist position. They can't possibly be with the rest of us, because that would mean living civilly and by the law within a society. This being a great example of their hypocrisy on display since a 'Person of Color,' a Hispanic, was the officer in this situation, not a white guy.
The other half is with the explosion of immigration ironically egged on by their boy Obama, American blacks haved diminished in status, and they are still living in the Black Pather glory days of the 60's. They are deathly afraid of losing their Preferred Minority status in the liberal kingdom, so they have to get more radical to stay on top.