There is obviously no better candidate than Harris for black youth turnout among the prospects (there is no other possible Obama)
How is Harris the best candidate for black youth turnout? What has she done in her political career for black youth? You say you're acting like she's not owed votes but what has she done to earn these votes that you declare them to be going into the Harris column?
Because she's black. The black people get excited about a black candidate and in turn show up to vote for said candidate.