Because he's not a good head coach. He's well under .500 when he doesn't have the greatest player in the history of football playing the game's most important position. A sub .500 coach probably isn't going to produce more great coaches.
Belichick is an all-time great defensive coordinator, but it's extremely evident that Tom Brady carried his offense for 20 years. That's why Weis, McDaniels, Patricia, O'Brien, etc. all sucked when they moved on. And all the defensive assistants that moved on suck too, because they no longer had Belichick himself.
Because he's not a good head coach. He's well under .500 when he doesn't have the greatest player in the history of football playing the game's most important position. A sub .500 coach probably isn't going to produce more great coaches.
Belichick is an all-time great defensive coordinator, but it's extremely evident that Tom Brady carried his offense for 20 years. That's why Weis, McDaniels, Patricia, O'Brien, etc. all sucked when they moved on. And all the defensive assistants that moved on suck too, because they no longer had Belichick himself.