Maybe I'm wrong, it wouldn't be the first time... but I sensed that the issue didn't just extend to what can be actually seen on the movie screen (actors/actresses). I think that the concern involves this premise that African Americans in general aren't given many opportunities involving all areas of movie production, from screen-writing, to producing, to acting - the entire lot.
And based on what I've seen and sensed in the 25+ years that I've been an active moviegoer - I think the concern is justified.