Scan the crowd of an NBA game and you'll see pretty much the same. Same with the NFL? Maybe it more ticket prices than disinterest?
I think one of the big reasons why we don’t see blacks at baseball games is that integration destroyed the negro leagues, which were the baseball outlet for black fans for half a century. When the Dodgers left Brooklyn their fans didn’t become Yankee fans. I think the same applies here. Fans of the local negro league team didn’t become fans of the local major league team. That trickled down 60 years now to the point where baseball is less favored by young black athletes compared to basketball and football.