I guess the Packers making the playoffs for eight consecutive seasons and assistants not being allowed to interview with other teams has factored into most of the team's assistants not being highly sought after.
Perhaps, but in seeing a couple of articles in the last couple of years which rated assistants, and gave comments on which were considered the highest rated and most likely to end up as head coaches (rated by other personnel people around the league), I don't remember any Packer assistants mentioned highly.