1. Historic Powerhouses (Ohio State, Wisconsin, etc.)
2. Non-P5s benefiting from easy schedules
The thing is, BYU has the most resources of all the non-P5s and has yet to reach that benchmark. It is frustrating to look around and see all these other programs make it.
Your percentages are mathematically correct, but don't tell the whole story. BYU should be on the upper-end of the bell curve when compared to other non-P5s.