The NBA is interested in the highest possible basketball talent. In the US, if you're good at sports, chances are you'll be noticed by the time you hit your teens. If your background is disadvantaged you have a pretty good shot of "making it out" as an elite athlete because colleges will notice you in time to avoid falling into the stereotypical poverty traps (gangs, drugs, etc). Basically, pro sports has a pretty good system in place to find the best candidates no matter where they come from so it's likely black men aren't over represented, they are mostly the best possible candidates out of the entire US.
There's also the point that, for some cultures, "making it out" due to becoming a sports pro, is seen as cool. Trying to "make it out" by actually working hard in school, getting a job early, gaining experience, etc.. is looked down upon. In fact, for the latter, in some cases the person will be bullied and derided for doing that.
It's not just on the colleges/businesses to recruit. These kinds of attitudes need to change.
It's part of why you also never hear cries to diversify or balance out things like pro sports either.. those doing the complaining about businesses and all are pushing for quotas for specific groups in specific areas, not equality across everything.