And yet we see world class players flop as managers. Can't remember the last world class player who successfully went on and became a world class or even successful manager.
The theory is it's much easier/more common for the mediocre player to succeed, because they had to work harder, think things through/find angles more. Whereas the superstar naturally had so many gifts, it's hard to translate what came so naturally to them to players who aren't similarly transcendent.
Also, just numerically, the average Joe anonymous midfielder isn't going to be handed jobs or even interviews, will have to constantly prove himself and fight his way up the ladder (manager-wise). Cream rising to the top, etc.