There was an incident in the month of April 1992, when a jury from Simi Valley let go free four policemen, accused of beating of Rodney King, which was also recorded on a video. Although there had been a wave of anger on national level, accompanied by huge scale riots, any other outcome of the case would not have been feasible for USA, which prioritizes order over justice. To accept the officers to be guilty, it would have been essential for the people to accept the grudge among black people regarding cruelty of police against them, which was unprecedented.
The same situation persists today, with a lot of people being exposed to offensive behavior from police. Few examples include the killing of Stephon Clark by police in Sacramento, shooting of Daniel Shaver by police in Arizona while he kept asking for mercy and a video captured by security camera, which shows six policemen hitting an unarmed suspect. Although there have been a lot of attempts by youth to fight this by rebelling and by various ballplayers, the topic of interest for people from all strata is not this, but other unimportant matters.
The current hierarchy in sports involves white coaches, white owners, white ticket buyers, white media and only black players. The media has failed to cover this and other aspects of this situation, due to the mindset similar to that of jury from Simi Valley two and a half decades ago.
In a situation where the rules regarding national anthem are made by white people, white coaches who very rarely manage to understand or assist black people, white people who buy tickets and white media covering the entire situation, it is not possible for a large chunk of people to consider the flag different from the police, because in the scenario of restraining the culture, police is indeed the police.