You can't do anything without a car in Texas border counties. They don't have public transit, but they have a ton of mom and pop restaurants. Or that's how it was when I visited my mom when she lived there.
So I don't think it's cars. It's something else, probably more of a home cooking tradition/habit, as others have pointed out in this thread. If you eat a great deal of home cooking, and Hispanics still have a big tradition of home cooking, then you're less likely to find chains appealing.
People who do home cooking tend to buy ingredients, not "meals." We don't buy that pre-done meal in a bag and heat it up--I can guarantee the people buying those are people who eat at chain restaurants. Traditional home cooks know that it's far cheaper and healthier to buy your own meat, veggies, grains, and so on. I mean, I tried one, because there was a decent coupon that made giving it a try worth a go.
I didn't make that mistake again. The salt content alone was gag-inducing.
Home cooking makes a huge difference in flavor and quality of the food. The last time I ate at a chain, because my mother was paying and insisted on it while we were traveling together, the food tasted like something heated up from frozen. There was too much processed crap, too much salt and grease, and, worst of all, too little flavor. It doesn't taste like the same dishes made from the fresher ingredients home cooks or mom&pops use.
Chain food tastes, well, like that meal in a bag that I stupidly tried, long ago.