Here's why. Obviously there CAN be upsets, but the ACC and BIG have so little crossover with their top teams it would take some major upsets to take teams out of contention. The projections oit right now with 2 B12 teams likely assume BYU and ISU will be favored in and also win the last 4 to 5 games.

BIG has 4 teams right now. Oregon and PSU are near locks as even with a loss both likely get in. Indiana has an easy schedule, likely 1 loss so 11-1 IU. Ohio State is the one that could fall out or also win the league. 3 teams pretty much guaranteed, potential for 4. If Ohio State handles Penn State and Indiana you easily could have 4 BIG teams with 1 loss or less

ACC is as problematic as you have 4 teams at 1 or less losses. Pitt or SMU play this week and Pitt plays Clemson, but Miami doesn t play anybody and Clemson only plays Pitt.
Best case here would be for SMU to beat Pitt and Pitt to beat Clemson and SMU to lose in the CCG. The overall issue is just this league has a lot of close games but these 4 teams havent lost in conference

SEC is probably the hardest one because a 2 loss SEC team will probably(I say probably because we dont know for sure) be ranked ahead of 1 loss B12 or ACC teams.Everybody has lost already but the still have Georgia, Texas, Tennessee, LSU, Alabama, TAMU, and Ole Miss in the hunt. There will be some attrition when teams get to 3 losses, but Texas and TAMU play each other but the dont play other ranked teams, Alabama plays LSU so one will drop to 3 but the other doesnt have any other ranked games, Georgia and Tennessee play each other but no other ranked teams. So issue with SEC is if chalk holds( it doesnt always but if it were) you d have 2 1 loss teams and 3 2 loss teams going into the CCG meaning one of your 1 loss teams would move to a 2 loss team. Thats 5 SEC teams with 2 losses or less.