Because of 2 reasons.
1, Mainstream media. As all of us have known since 2016, the mainstream media loves to feed into SJW's and Communist's delusions which not only can be seen in the death of George Floyd but also can be seen in cases like Breonna Taylor's death, dipshits at ABC, CNN, NBC, NPR, etc will push the lie that the cops who killed her were at the "wrong house" when in reality they were at the right house and another thing they will lie about is saying that the raid conducted at her apartment was a "no-knock warrant", if you did some digging into it you would have discovered that police did knock.
2. Politically biased. Almost every mainstream media service is biasedly left-wing, this is not only seen in Breonna Taylor's and George Floyd's death but is also seen with the winning of Donald Trump in the 2016 election where a lot of them pushed the bullshit Russiagate conspiracy theory and falsely claimed that Russia "stole" the 2016 election, another thing that the mainstream media will do it cover for Antifa and BLM and claim they are "fighting racism and fascism" when in reality they can be just as racist and fascist as Oswald Mosely's blackshirts and the KKK.
