Mark Harris went over there as a kicker. They loved him because not only could he kick the ball huge distances, he could be there to tackle when the ball came down. They'd not seen any kickers do this. NFL players can be one trick ponies, just doing one thing really well. In NRL you don't survive without a wider skill set.
AFL players have become more popular recently as punters in NFL (particularly in one team ... I can't remember who) because they have the skills to run the ball, evade defenders, and kick accurately off both feet. This gives extra time for defenders to get down the other end of the field and increases yards gained.