If you were not recommended but are within the zone of consideration you should receive counseling from your first line leader. During this counseling, it should be made clear why you were not recommended for promotion. See AR 600-8-19 paragraph 5-10:
Although all Soldiers may be eligible to be considered for promotion, only those Soldiers recommended by their immediate CDR per paragraph 5–8 will be referred to the selection board. SGTs and below who are within the zone of consideration but not recommended for promotion by the immediate CDR must be counseled by their first-line supervisor. They will be advised of the reasons for not being recommended, current deficiencies, and the ways of improving their performance. This mandatory counseling will be directed toward those areas in which the Soldier needs to improve in order to be recommended to the board.