tbh it really runs into people's subconciousness, perhaps alot of white people are glad to see white heavyweights controlling the scene....Its only natural that a white non-boxing fan is going to route for the white fighter if there was a match between a white boxer and black boxer.
It may be a prick on some americans ego's that there are european champions, but that isn't unexpected because for the past 100 years they were the superior to everyone else in regards to the sport.