Parrot I believe the better question in this Amerika is WHY big White guys do not pursue the route of Heavyweight boxing? That is the question. Most CFers know the answer. A clue; the DWF mentality.
West, you know the answer to this. There are simply not enough gyms with good trainers around. And where there are gyms with competent trainers the guys just aren't coming in and trying to learn the craft. In the East they have extensive amateur programs and the culture of boxing/fight sport is favourable. More men there love the sport and are dedicated. In the USA the culture and programs are not there.
It takes a long time to make a champion or, at least a good pro. I'm a part time trainer (I can't make a living doing it). And it is next to impossible to find anyone who is willing to take 5 years to learn the ropes. Typically a guy will train for a few months to a year and then be satisfied that he has some skills. A lot of the men that make it to the top had a father or relative that could train them. Look at Cleverly, Garcia, Fury, Ward, and even Mayweather Jr. They have fathers or uncles that know what they are doing. I don't see things changing anytime soon. On the other hand, the USA has the very best skateboarders anywhere!