Of course you are right. Most here understand that. What we see is what people choose to show and the comparison pics are mostly real. Simply put a guy with a big one is more like;y to show it off. I give you an example from years of personal experience in locker rooms. I think this is true. Porn and sites like this and threads like this make smaller black men even less likely to show what they got because we have all heard the stories for years about black men.
In the locker room, if a black man gets nude chances are he's hanging, chances are also good that for each one that does go nude there is another who doesn't because he doesn't meet the expected stereotype. White guys including me don't have any myth to live up to. So we see and show all sizes. With more white population plenty of white dudes will get naked with a small or average cock and you see a lot of them. The small black man makes sure he is never seen nude, where white men who are small don't care as much because we see peers who are similar and we don't have a deeply ingrained "myth" to measure up to.