Black people, who disproportionately consume social services, obviously disproportionately vote for the party who pays for those social services. So Black votes are guaranteed Democrat votes.
I can understand why they would want Black people to come out to vote to begin with if Blacks are not voting - and that is because, as explained above, that outcome is a guarantee of more Democrat votes.
That's the same reason why Democrats in the USA [and Liberals here in Canada] want to continue to import non-Whites from all over the world - because once these people come to the West and consume social services at rates vastly higher than White people do, you end up getting more votes for the Democrats in the USA and the Liberal Party here in Canada.
The only problem with this model, unbeknownst to left-leaning people in either the USA or in Canada, is that eventually the social welfare states in either country are going to collapse as a direct result of this.
So to lefties - good luck pushing your welfare, free healthcare, free everything for everyone model, when you run out of money to steal from other people to pay for it.