If we’re within two games of any ACC team we can take their spot in any ACC affiliated bowl game with the exception of the Orange Bowl. The ACC is guaranteed a spot in the Orange. We can still get a spot in the Orange as long as SEC and Big X don’t qualify. (They qualify if after filling their spots in the CFP, if applicable, and then the Sugar and Rose, respectively, they still have a team ranked higher than ND in the final playoff rankings.
The Sugar and Rose have guaranteed conference affiliations and ND cannot play in those games. Normally, ND could take an at large bid in the Peach or Fiesta but this year they are CFP semis, so they are not available. That leaves only the Cotton this year as the only game available for at large bids. One spot is guaranteed to the highest rank Group of 5. That leaves only one at large spot available.
That is why an 10-2 ND will not be in a New Years Six game this year.