They don't matter to other blacks, they don't matter to politicians (until they're needed as voters), and they don't matter to most Americans. Their snappy slogan is the purest form of racism as well as a means to extort money from weak minded corporations and gullible white college students who were never taught by their parents how to be decent human beings that can function in a civilized society.
It's a catch 22. Yes, black lives matter, just as Asian lives matter, Hindi lives matters, and white lives matter. But to say all lives matter is considered racist by BLM, therefore BLM is racist.