I am a african american and I took up distance running 20 years ago.
The reason why most young african americans do not play soccer, or hockey, or even become middle distance runners is because most of our sports heros were football players, backetball players, some baseball players, and sprinters.
Those are the sports you play, watch and see as a african american youth growing up over the last 30 years on your local playgrounds, parks, neighborhoods, etc.
I took up middle distance running because I figured that since I was a naturely fast runner (sprint races in the Hood, basketball, football, etc) and my mother was giving me a hard time about football that maybe cross country would be great.
I loved it and then tried track. It was natural for me. I didn't really train but I ran 4:59 for the mile that year.
I didn't RUN AT ALL DURING THE summer and still ran around 16:30-16:45 for cross country and on 25-30 miles per week ran 4:33 and 1:59 for the mile and 800 my soph year.
What I am getting at is that we (african americans) do have the mental toughness to be very "GOOD MIDDLE DISTANCE/DISTANCE RUNNERS" if we chose to, but in your youth you are exposed to your sports role models (many from you neighborhoods) doing very well in the other sports and making alot of money, fame, etc.
PS. When it can to Track & Field we were not seeing alot of Americans on t.v during the various Oly games winning anything (other then Bruce Jenner) but we were seeing alot of African American Males/Females win Gold in the Sprints and Jumping events. Those moments leave a lasting footprint!
Just my viewpoint as a african american runner and former middle distance runner.