I thought a lot of this interview with Darius Butler was really good and insightful, especially on the point about why there aren't more Black coaches in the league. At about the 7:30 mark, he talks about why he would not want to go through the pains of being on the bottom rung again of being a coach, and how most of the problem is that years of playing experience is not usually taken into account when deciding if you will be a coach. You have to go back to grinding and putting in your dues, which generally means you have to start out putting in 10x the number of work hours than you did as a player. Many former athletes don't want have to go back and start that kind of grind all over again. And as been pointed out, most of the former players are black. And frankly, regardless of race, many players that are the best at what they do sometimes make poor coaches.
Many coaches in the NFL, head and assistant, were unathletic white guys that were never good enough see the field ever, or never beyond college. They go immediately into coaching because that is all they can do to stay with the game they love. They start the grind of coaching at grad positions at 20 years old, eventually working into higher positions by their 30s. Exceptions are the football savants like McVay. White guys couldn't play, so instead they coach! Stetson Bennett is not going to be good enough to play in the NFL, so he is probably going to head into coaching. So there's another white guy for the mix!
https://www.youtube.com/watch?v=tpOX2SOH2j4