They can't get 4 good teams to play them. Last year their AD offered to play anyone, anywhere with no return trip, and they didn't get any takers.
They did what they could when they decided to go to the MWC, but then BYU and Utah decided to leave so it looks like they'll largely be in the same situation (except with an annual game against TCU).
If they run the table this year, they'll be riding a 27 game winning streak and be 39-1 since the start of 2008, with the only loss being by 1 point to TCU in a bowl game. If you put up those kinds of numbers, I don't care what your schedule is - you've earned a shot at a title.