Because, after all, that's the most important thing. 

Via Reuters: 

U.S. President Barack Obama said on Sunday that attacks on police out of a concern about the fairness of the criminal justice system hurt the Black Lives Matter movement, after a sniper killed five police officers in Dallas on Thursday.

Obama told a news conference in Madrid that although the "overwhelming" amount of activists in the Black Lives Matter movement wanted to see better relations between communities and police, there were always people that say "stupid" things.

The sniper, Micah Johnson, a black U.S. military veteran of the Afghan war, said he wanted to "kill white people" following the fatal shootings of two black men by police in Louisiana and Minnesota.

No, the overwhelming amount of BLM folks don't want better relations with the police, they want to eliminate police. They say it on their websites, in their literature and in their chants. Chanting 'what do we want, dead cops' is not just a 'stupid thing'. Killing and injuring police, rioting, burning down Ferguson and  Baltimore are not just 'stupid things'.