BLM limits the scope of its slogan to a small number of black lives. Those killed by police, and that can be used to further leftists causes. At the same time it expands its agenda to include unrelated issues like marxism, nuclear family, geographic disputes in other parts of the world, etc. When criticized, it falls back on the plain meaning of its slogan, and vilifies the critic as racist. And makes out that they're saying black lives don't matter.