SMU is a very small, private school in an area that has been intentionally geographically isolated from the rest of Dallas. It's not academically elite, but its student body is incredibly elitist—grandpa's oil money, which is still "new money" but old enough now that the grandkids think they should be "old money." The students are obnoxious, and the school just isn't relatable to the rest of Dallas, which (outside of Preston Hollow, Lakewood, the M-Streets, and a few other neighborhoods (mostly around Whiterock Lake), is surprisingly gritty.

TCU is also a private school, and seems to attract a lot of students from outside of Texas. In my anecdotal experience, it's where out-of-state kids go after they realize that state schools (especially UT and A&M) cap out of state enrollment and are expensive for out-of-state kids (limited scholarship access; huge tuition disparity between in-state and out-of-state tuition). A lot of their grads seem to leave the metroplex after graduating and, regardless, it doesn't have a lot of appeal in Dallas. Even during their undefeated season and playoff run, it was rare to see TCU swag, and they aren't the primary team for very many people.

If anything, Dallas is much more split between UT and OU than anything else.