I don't know why. Coheley seems to have the best answer. Kids today like more fast-paced action like they get in football and basketball. Baseball is too slow for them. There's more standing around than there is real action.
Kids have more options.
And for most black kids, baseball is not their sport of choice. So these kids grow up wanting to be like Mike. Not like Bonds and Griffey. Unlike football and basketball, baseball is not a sport you just take up in high school. Hakeem Olajuwon was a Nigerian soccer star with little basketball background when he showed up on Guy Lewis' doorstep in Houston, but he had the athletic skills needed to begin his basketball career late in life.