"Black lives matter" is a desperate cry for help from people subjected to the deadly violence of the police and of racist "neighbourhood watch vigilante wannabes" (killing or Trayvon Martin) or straight up lynchers (killing of Ahmaud Arbery), to demand "stop killing us".

Now imagine responding to that "No! No! ALL Lives matter."

People saying all lives matter are either that stupid to believe it means only black lives matter or that malicious to pretend it does when it was never implied.

I don't know how to explain it better if you still don't get it. It's kinda like if I was passing through a famine stricken country and people dying from hunger told me they were hungry and I went "Well, everyone's hungry" before turning a deaf ear to their suffering. It's that disgusting.