It's true that USC and Notre Dame did cancel their series for the 2026 to 2029 seasons, but I'm sure you know that those games are on again for 2030 through 2033.
If anything, that should illustrate to you that athletic directors aren't the only stakeholders when it comes to non-conference scheduling. You have fans, alums, ex-players, tradition, conference officials, sports writers and the holy dollar (television networks) at work here.
I suspect part of the calculation by USC here is that the CFP will be expanded to at least 16 teams by 2030. We all know that Pettiti along with the ACC and Big XII want to go to 24. That makes playing Notre Dame in September each of those four years (a concession by ND) less of a problem. In fact, those talks with ESPN on CFP expansion may be starting today. See:
https://www.sportsmediawatch.com/2026/09/cfp-espn-talks-24-team-expansion/
I rather suspect that when SEC expansion caused the Michigan-Texas schedule scramble, guarantees were made to ESPN IRT the 2027 game in Austin. As I wrote before, I imagine Manuel doesn't operate as the sole arbiter of Michigan's non-conference schedule.