Their fullback averaged 4.2 ypc - that is not a good number, by the way; you seem to think that it is. His long carry was 8 yards, meaning he averaged about 3.8 ypc on his other 8 carries. In fact, each of their top 3 rushers had one good carry and then were unproductive on the rest of their rushes.
They did not consistently pick up positive yardage up the middle. They picked up positive yardage up the middle here and there.