They sure put a lot of effort into enshrining chattel slavery into law and preventing its destruction. It's the only state to secede from another nation twice to protect slavery.
If you want to keep digging, you can add American expansionism and ambitions to conquer big parts of Mexico, i.e. a "manifest destiny" land grab. The US was happy to tacitly support the Texans because whether they failed or succeeded it was relatively low risk for the US government and their success was likely to further US interests.
It's also fair to say that Santa Anna was a proto-fascist and that was a legitimate factor, not a convenience. Lorenzo de Zavala, the former Mexican finance minister, didn't become Vice President of Texas for slavery or American expansionism.
But Texas anglos didn't really give a shit about any of that. They just wanted to left alone to build their own little profitable slave plantation economy modeled after the US southern states.
The periods before and after Santa Anna were also very violent and politically unstable, with armed rebellions all over Mexico. Santa Anna was fairly ordinary in his goals and methods by the standards of Mexican/Latin American caudillos.
The fundamental problem was not one or another particular person, but a society organized along quasi-feudal lines with extreme wealth/power concentration and systematic repression by elite landowners and a central state with limited power or legitimacy and huge logistical challenges. If it had been someone else other than Santa Anna in charge of Mexico, Texas anglo slave owners would have still had the same motivations and more or less the same systemic context, as would the US government, and eventual outcomes would have likely been similar.
I would be shocked if that was true.