4 heavyweights with 3 things in common, I'll give you 1, which will leave 2.

[greynotsoold]

I'd guess one being that none of them ever got a chance to fight for a proper HW title, they were avoided by the likes of Dempsey or whichever other white champions? No clue as to another.

Actually, I think that Langford, McVey, and Jeanette were avoided by Jack Johnson. He was black, too.