A few comments on this.
Texas tried for decades to get Michigan and Ohio State on the schedule for a home and home. Those programs did not want to come down to Austin in September. There were talks of making the game later in the season, but with OU locked in, and neither program really wanting to interrupt conference play, they couldn't work it out. That's why Texas hadn't played either program in its history until the 2000s.
There was a time when Texas was trying to play Notre Dame as much as possible, but the Domers didn't want to lock in their schedule with Texas with so many other teams they wanted to play regularly. Heck, there was a time when Deloss Dodds was under the illusion he could get Notre Dame to join the Big 12 to replace departing teams, or at the time teams that were threatening to depart.
As far as us not playing A&M hurting college football, did it really? One of the qualities I really admired about Dodds was his sheer pettiness. I loved that he refused to play UH in anything after Bleachergate and the whole debacle that led up to it. I loved that he refused to play A&M in anything after they left for the SEC. I think this is the right thing to say, but if we ever left the SEC for some reason, it wouldn't bother me not to play the Aggies any more.
And no one actually cares about OU/Nebraska any more. I get a little nostalgic about the great games in that series, but I'm old. Those games haven't been any more relevant to college football for a long long time than the Arkansas/Texas battles of the 60s.
Also, we do have Arizona State as the marquee game in the future. If Dillingham is still there they'll have something, but otherwise it's a trip to Phoenix. Not a trip to play the Sun Devils. The chances of that matchup mattering aren't great. But that game will be played at the edge of my mortality, if I even make it that far, so I'm not terribly concerned one way or another.