The Japanese internees got reparations because many of them were still alive. None of the slaves are alive, none of the people that owned slaves are still alive, and nobody has any public interest in reverting to a slave system.
As for "but the blacks are still being enslaved by everyone else!", I shall quote David Eddings:
'"You've enslaved us!" someone bellowed.
'"Not me, old boy," Stragen drawled. "You couldn't *give* me a slave. You
have to feed them, you know - even when they're not working."'
One of my favorite authors, which book was that?