The Gophers need more sacks, TFLs, and interceptions. Those are the things the voters look for (right or wrong). Mafe made the 2nd all-Big Ten team because he had decent sack numbers. But, he wasn't the Gophers best defensive player this year. He was good, but was not our best defensive player, but he led us in sacks and TFLs.
Gibbens had a stellar year, but the Big Ten is full of great LBs. There are LBs from other teams with more tackles than Gibbens who are not in the top 9, either. Gibbens was 18th in the Big Ten in tackles and had no sacks.