Who said that black footballers wanted to become managers? Maybe they arent interested in such an unstable job. Fair play to them if they arent interested.
This might be true. On the flip side, there may be some ingrained institutional racism which nobody is even aware of. There was in American Football and the Rooney Rule was a real solution to it. Perhaps it may be in English footy. The stats are a bit weird with so few making the step up. Perhaps you're right but there's literally no harm whatsoever in trying.