Because nobody doubted for a moment that there were non-violent members of that mob.
Not to mention that it is still evidence. Maybe they were afraid some loser would take it, remove all the violent scenes and then try to present that as proof that it was peaceful.... Wait
Or that once that video was made a whole buch of suckers and liars would start presenting it exactly as such.... Wait
By the way. I have proof that there was never a violent moment at a "BLM" protest.
See? Now I have proof that there were not then, or ever, violent destructive protests blocks from there.
You Have Seen The Proof Now! You must be itching to spread this all over the internet!