I'm sure it's heavily weighted toward recruiting rankings at this time of year, and recruiting rankings are often garbage. Gabe Jacas was a no name 3 star committed to Tulane before flipping to Illinois (was also pursued by Temnessee, iirc) and is now an All-American Candidate. He's still counted as a 3 star in the formulas that consider recruiting rankings, which clearly shortchanges his talent.
I'm sure it also doesn't account for coaching, and Bielema has shown that he's a darn good one, while coaches like Manny Diaz (Ron Zook's spiritual successor) have shown they'll find ways to lose games