I can think of a good reason: Northwestern in 2018. Sure, they lost in the CCG, so no harm, no foul. But they lost to Akron and to Hamburger University and to Evanston Elementary School for the Blind. They also lost to Sparty's little brother. But they won their division. I think going 8-4 is enough to keep a team out of any playoffs. If they had found a way to beat Ohio State in the championship game, it's bad enough that they would go to the Rose Bowl (if the Rose Bowl wasn't a playoff game that year - I forget if it was), but to go to the playoffs cheapens the playoffs.
Also, and along the same lines, why would a team even need to try very hard to win their OOC games? All you need to do is win your conference games, and you're in the playoffs.
I agree that it's hard to lose your CCG and still make it into the playoffs. The SEC can do that because they're THAT good. But just saying that if you win, you're in the playoffs, I don't like it. Mathematically, a team could lose 3 OOC games, then go 5-4 in conference play and tie for the division championship. I suppose they could even go 3-6 and tie for division championship (all teams in a division win at home against other division opponents, and all teams lose their games against the opposite division). All teams would be 3-6 in the conference, and you have to pick a winner. So, a 3-9 team could be in the CCG. Then they magically win their CCG. I know all of that is extremely unlikely, but I don't like the fact that we have a path available for a 4-9 team to be in the playoff.