Indian Americans have a special affinity for Taco Bell for several reasons, I've noticed, including those that the previous responses already addressed.
- There's a wide availability of vegetarian food options at Taco Bell, and it's one of the few fast food chains that's vegetarian-friendly. (Lots of easy meatless substitutions, even for meat entrees.)
- Taco Bell food appeals to Indian tastes. Tortillas are similar to Indian flat breads, and the beans are similar to typical Indian foods. The food can be made spicier with hot sauce. My parents usually grab 10+ fire sauces before sitting down to eat their two tacos.
- It's a relatively inexpensive dining option, cheaper than a lot of other fast food. Indian Americans are, ahem, stereotypically frugal. We like Chipotle too, but that's a bit pricier.
- The facilities are usually larger, cleaner, and less crowded than some other fast food places. We are fussy people.
- The restaurant has cemented its popularity among Indian Americans, at least in my community, by becoming something of a gathering place for local Indians, especially high school kids and families. About half the time I eat at the local Taco Bell, I bump into someone I know. Indians like to eat where they can socialize with other Indians. It's become a tradition.
In my experience, Indian Americans like "Mexican" food in general. In my family, Mexican is probably our default option for eating out, more than Chinese, Thai, and Mediterranean. Taco Bell is only pseudo-Mexican in the vaguest sense, of course, but a cheap and convenient alternative to the real thing. Strangely enough, I've heard that Taco Bell isn't nearly as popular in India...it must be a diasporic thing?