Because Iowa had a 3 back by rotation. Goodson was the workhorse the last 2 games and was great. Hall is very good, but so is Goodson.
Goodson 134 attempts, 638 yards, 5 TDs, 4.8 ypc
Hall 186 attempts, 897 yards, 9 TDs, 4.8 ypc
Hall had 50 more runs that Goodson and the same ypc. Not hard to see how Goodson being the workhorse will be a good player. Both were freshman. Both played vital rolls in their teams success.
Not sure if Hall got dinged up, but I do know Goodson was dinged up for a few games this year.