Joe Morgan was dismayed to find that there were so many blacks in these sports. "There must be some way to get more whites to fit the quota. It sends the wrong message." Yeah, right. Joe Morgan, once a racist, always a racist.
9% is in line with the proportion of blacks in the general population. If the black athletes with skills in 2 sports choose against baseball, there's nothing to be done there. I'm no expert, but my guess is that it takes a long time to get to big money in baseball. A star basketball player very rapidly gets to the big paydays. Ditto in football. The free market is working in its mysterious ways.