This Purdue offense is not going to be proficient in running the ball, but being able to run the ball even just a little makes a huge difference. The games with the highest rushing yardage and yards per carry (UConn, OSU, Iowa) are the games where the offense scored the most points. The games with the lowest rushing yardage and ypc (Wisconsin, Illinois, ND, Minnesota) are the 13 pointers. And the Wisconsin game with negative rushing yards, a defensive TD was required to get there.
Oregon St 88 yd (2.7 ypc) = 30 points
UConn 187 yd (4.5 ypc) = 49 points
Notre Dame 57 yd (2.3 ypc) = 13 points
Illinois 38 yd (1.5 ypc) = 13 points
Minnesota 77 yd (2.3 ypc) = 13 points
Iowa 86 yd (2.6 ypc) = 24 points
Wisconsin -13 yd (-0.5 ypc) = 13 points
A lot of this is on the O line. All that is needed from them is just to be serviceable in the run game. And they've been serviceable 3 times and good exactly once, not coincidentally against an over-matched UConn team. Horvath is maybe the most important player on the offense because he can grind out yards on his own. He isn't a home run threat, but he does enough to open up the field for passing. His loss has been huge.
People like to talk about Tiller, Brees, air raid, etc. But the run game was never this poor. Any Big Ten DC worth his salt will figure out how to shut you down if he can stop the run without even trying.
The good news is the bar is not that high. Like, not high at all. If I told you all we need to do is figure out how to get 80 yards of rushing against Nebraska and we'll be in pretty good shape, that sounds like a pretty good proposition, right?