Many sports are white dominated (that is the people playing at least meet the same representation as in the US population that is about 75% white depending on the definition of "white") and wanting to attract people of color, especially youth.
I would say don't worry about getting kids (pre-high school) into distance running. Keep them active and develop their athleticism and also the socialization of team sports. This is to develop physical literacy.
Distance running is seen as boring by a huge number of people. It can be! It also has a lower cool factor that lots of other sports as well. It can have a lower social aspect too. You might be on a team but when you run you end up alone in a many cases. Most people are extraverts and want to be around others. Obviously a big team reduces the running alone aspect.
If a team is all white and a black kid sees that it is probably very intimidating for that kid to come over to join in. Tons of sports have this issue. We can say "we welcome all" but in reality the black or brown kid might not think it is real. They may have had bad experiences being on the only black kid doing something.
Even the vast majority of black kids in a niche sport will still not be "great". I think that approach is actually a bad one as it sets up a false end goal. How about developing an intrinsic love for being active versus chasing an extrinsic reward. The top athletes have that intrinsic love for what they do. Kids may dream of playing in the NFL (who hasn't?) but they stick with a sport because they develop a love for it. Once the love for the sport goes away they leave or if they are being coerced into staying (see Todd Marinovich and Andre Agassi) they develop mental health problems and sometimes drug addictions.
I would even broaden the discussion to lots of white kids who could be good runners and maybe fall in love with it. We don't see them in running either. Part of me thinks it is because running for the sake of running at some point seems boring. Part of me thinks that parents often have so structured the play of kids that kids don't just run around for fun as much. Rather than getting together with the other kids in the neighborhood and chase each other around (which is a lot of fun) parents drive them across town to stand around on a soccer pitch touching a ball every once in a while. Kids get bored and find things that they want to do and that parents won't interfere with (video games for one thing).