Really? REALLY? The Negro Leagues in the grand scheme of things is very little significance in American History. Sorry. Not everyone needs to know every example about segregation. People in America are taught a SHIT TON about the civil war and about abolitionism and about slavery and the fine folks that fought against it for hundreds of years.
You might as well say that kids aren't taught enough about our Independence because they can't recall everyone that signed the Constitution. That's bullshit and you know it. Americans are taught, to a fault, their own history, non-stop from K to 12. We do NOT ignore black history AT ALL. Not even a little bit. It is a HUGE portion of our history and a huge portion of what is taught in schools. Do they teach everything? No, of course not.
And, guess what, the Negro Leagues is AMERICAN history, not african american history. To only teach one side of that story would be missing out on half of that subject-matters significance. You didn't confront a single point Morgan Freeman was trying to make.