The whole point of it was to acknowledge discrimination as a whole, not to pin point discrimination against a specific group then take baby steps towards a future of equality.
In America it is clear that whitelivesmatter because you don't see police officers killing them for existing. However, that's not the case with black people, they're discriminated against and killed every day without the government or society demanding a change. That's why #BlackLivesMatter it's a way of reminding authorities that they deserve to be valued and respected as much as any other person.
It's a cute distraction tactic to pull attention away from the continued, if not systemic, murder of Black people with little to no consequence or retribution from the law.