Could be lots of reasons for it, don't know, but the Jags offense sux this year just from glancing at their record. 29th in Scoring, 32 in Total offense.
First of all, we all know College Success ≠ NFL Success, but just having that NFL experience is invaluable (See Saban, Petrino, Spurrier).
His 1997 Oregon team broke school records for offensive production. Put Boise on the map, as mentioned. His 2005 Offense at Arizona State was 2nd in the nation.
When he had a decent QB in his first year in Jacksonville, he improved their offense from 10th in the league to 7th. This year he's working with a rookie QB and no WRs.