Cause they already said before that there is a chance that NO ONE would be promoted to chuunin even if some win and it is decided by the judges who choose them by who have the skill or leadership to be a chuunin. Therefore, by comparing the competition and their usual ninja tasks, good leadership skills like Shikamaru has who are able to give up the competition (meaning that he could give up their actual ninja tasks in trade safety of his teammates)are needed and not like Naruto, who screams and charges straight towards the enemy most of the time and jeopardizing the entire team-mate population and could get all of them killed.

If naruto and some win, how come only shikamaru get to be cuunin?