Per Texas AD DeLoss Dodds: "They left," Dodds said of A&M, which left the Big 12 and joined the SEC in 2012. "They're the ones that decided not to play us.
We get to decide when we play again." While the current Texas AD is much less of a tool than Dodds, this is classic Longhorn attitude. I love Austin, but the unbelievable sense of entitlement in the Longhorns' Athletics Department and fanbase makes that difficult at times.
From the A&M side, they have a strong case of "little brother." If you go on TexAgs, there are innumerable posts about how they no longer care about the Longhorns, but yet they still talk about them all the time. The rivalry wasn't exactly in their favor either - maybe some of us wouldn't mind taking a break from Alabama or LSU for a while***
On a practical level, A&M probably doesn't want another hard game on the schedule that includes their SEC West schedule. Texas has been scheduling teams like Notre Dame, Southern Cal and LSU and probably doesn't want to use that Power 5 non-conference slot on a game that, in their mind, provides less national exposure (nevermind that they A&M-Texas game was almost always the marquee college game on Thanksgiving when it wasn't the Egg Bowl).
Some fans on both sides seem to think that the higher ups want the renewal of the football rivalry to come in a big bowl game (at least one bigger than the Texas or Liberty bowls) and won't consider scheduling a home and home with A&M before then. The fact that both teams have been giving up a home game every other year by playing conference teams at neutral sites probably makes it less appealing, too (but I'd hate to see the Red River Shootout in Dallas go away, either). It's a shame this series hasn't been renewed.
"You can gig'em, you can hook 'em, one thing will never change: when your eyes are closed and you're in the dark, the colors are all the same..."
https://www.youtube.com/watch?v=YmZNmkklpRY