Open Question: Why did Jack Johnson avoid certain fighters?

Jack Johnson is one of my personal favorites because of his style and attitiude. ''The Galvaston Giant'' was a beast in the ring buuuuuuuuuuut, some people on here (u know who u are) have it in for Marciano (that he fought old men) and Dempsey ( that he avoided black fighters) But never is it asked why did Johnson avoid fighting,Sam McVey, Sam Langford (who Johnson had beat as a contender but chased Johnson for a fight much like Johnson did with Burns but never got a shot) Peter Jackson or Joe Jeanette. All whom were black. Jeanette even stated Johnson turned his back on his race when he won the title (Ken Burns book ''Unforgivable Blackness".) Johnson could have fought any of these great warriors in Europe or Cuba but never did. Can some1 give an honest NON RACIST answer to this question???? Why the double standard amongst some here in this forum? Like I said I love Johnson but it is a valid question.