The Spanos family is very loyal. The Chargers players wanted Norv back. If Norv fails to lead them to the playoffs he won't be the only person fired. AJ Smith will finally get the axe as well.
Well obviously veteran leadership is vital to a team's success. That's what Carson is. As for Norv he just wasn't a fit for SD without a great RB. He could not address the oline or how to deal with it like Rivers did.