The lives of Anna and her surviving children mattered, you see.
In the decades that followed, over 300,000 native Africans were forcibly brought to the United States. Their numbers were 4,000,000 by the start of the Civil War. For 100 years after Emancipation, they and their descendants were terrorized, subjugated, and deprived. Their lives simply didn't matter to most whites, you see. That's the hard, awful truth. It's not easy to undo that damage, and it certainly all hasn't been undone yet.
All lives matter; Christians and adherents of nearly every other religion would agree with that, as well as most humanists, agnostics, and atheists… probably even Ayn Rand in her own way. But when we say Black Lives Matter, we affirm two things: only recently have a large number of white Americans actually believed that, and too many white Americans still don't. Anyone who says racism isn't prevalent today is either naive or delusional.
And that is why Black Lives Matter, with capital letters.