The issue is the strength of the schedule. The P5 teams just have a bigger grind over a season. They face more talent week in and week out. BYU fans were crying foul that the Playoff committee didn’t have them in the top 10, but it was impossible to tell if they were a top 25 team with that schedule.
Yes, the occasional team will get hosed. But for the most part, the G5 teams are just not as good. Recruiting rankings are not perfect, but they’re fairly good indicators of team talent. No G5 team averages in the top 30.
Brand names will get the benefit of the doubt and can lose games and stay ranked. But by far the easiest path to a ranking is playing bad teams and winning.