Black on black crime has, long since,been a misnomer. Hispanics and Whites both commit at least 75% of their crimes against members of their own race. Its been proven that crime is ,generally, committed close to where the perpetrator lives (most people aren't traveling 100 miles to stick someone up). Blacks are much more likely to live closer to each other (think, inner cities or "the ghetto") therefore they commit the majority of their crimes against each other.
White supremacists have used it for years to attempt to discredit black movements (civil rights or BLM) Trump actually retweeted fake black on black stats that were originally tweeted by a neo nazi group.
That being said,people ignore the thousands of activists who risk their lives to try and make a difference in their crime ridden communities. People care, quite a bit, they don't want their kids being killed.
I'm not sure you understand the levels of mistrust by blacks and Hispanic towards police. Literally, for decades, Police have been tasked with enforcing laws such as Jim Crow. Often they used harsh tactics (like high powered fire hoses, and sicking police dogs on innocent people or using batons to beat blacks).
The police self police themselves and seldom face criminal charges for criminal activities. For example, a cop ordered a man to get on the ground . He complied and the cops kicks him in the face, breaking the mans jaw. There was dashboard footage of the assault but the cop faced no charges and kept his job.
Tamir Rice, the kid in Cleveland who was playing in the park with a toy gun was killed by a cop. He claimed he warned the boy 4 times to drop the gun but eyes witnesses, video surveillance and three different experts proved that he was lying . He shot the kid less than two seconds after arriving. He didn't even go to trial and kept his job.
Jonathan Ferell got into a near fatal car accident (He flipped his car over). He went looking for help, by knocking on a door. A woman assumed he was a criminal and called the police. The cops arrived and shot the unarmed man 10 times. He cop walked after a mistrial. The police department agreed to pay the killer $180,000 in back pay and agreed not to retry him.
This is fairly common place, interactions between blacks and the police. Keep in mind those above numbers don't include. Toy guns, rocks, or small knives. Many of those situations could have been resolved with a taser or non lethal weapons.
The McDonald shooting, fits that description. Cops actually requested a taser but the cop decided shoot him twice. After the kid lay bleeding to death on the ground, the cop continued to 14 times. The police there, then lied in police reports and their superiors covered
up the cover up. By attempting to block the dash board release and deleting video surveillance from Burger king.
Protesting the police doesn't mean that blacks don't care about "black on black crime" they care about both. The police is supposed to help the issues in the black communities by helping to reduce crime, instead, they treat every people there as if they are criminals and often react in heavy handed policing.