I am not suggesting that murder of anyone by anyone ought to be discounted.  BLM was formed in reaction to the disproportionate rates at which police officers shoot black men.  That is the issue that they are addressing.
I believe that the murder rate would be lowered if we spent more money on education to improve inner city schools, if we did a better job enforcing gun laws, if we offered more support for families in need, if  we had better after school programs, if we did a better job preventing teen pregnancies ....
It's not at all fair to suggest that BLM people don't care about black murder victims.  No one organization can address all of society's evils and shortcomings.