Would "I love George Bush, Jesus, and BBQ" fly?
On a serious note, tell them the following:
(1) You hate cold weather, especially after living in Chicago for three years. California's too expensive, and the work in Arizona and Florida just isn't as sophisticated as it is in Texas.
(2) You love Texas because you get to enjoy the big city lifestyle at about a third of the cost of California, Chicago or New York.
(3) Similarly, the quality of work is on par with those cities, and the comp is similar, but again, you get a lot more bang for the buck.
NOTE: The first of those is true but misleading -- the summer in Texas is far worse than the winter in Chicago. You're going to see a heat index around 115 no matter what -- the only question is if you prefer 95 with 90% humidity (Houston), or 105 with 50% humidity (Dallas). The second is just wrong. You don't have the same big city lifestyle in Houston or Dallas as you do in New York or Chicago or SF. LA might be vaguely comparable, depending where you live. Though the restaurant scene is actually pretty sweet, at least outside the high end stuff. Third, with a few notable exceptions (energy, maybe IP), the work isn't going to be comparable. That's why they seemingly overpay for associates. But to a true Texan, those reasons for wanting to go to Texas will make absolute, perfect sense.
Things not to say:
(1) Try to avoid coming across as a conservative redneck. Yes, a lot of the people down there are like that, but a healthy minority aren't -- and they disproportionately make up the professional classes. If you are in a room with three Texas Biglaw lawyers, probably at least one of them is going to resent that stereotype.
(2) Try to avoid indicating that you want to go to Texas for better hours. At a lot of firms -- especially the big ones -- they're not. And they are very wary about people who just want to go down there to work less.
Hope this helps! (FYI: I grew up in Texas but left for law school and never looked back.)