Taco Bell loosely belongs to (maybe better to say "is inspired by" or "owes origins to") a class of regional and traditional fusion food called "Texmex". It's a uniquely North American comfort food class that naturally developed over a long period of cultural intermixing along the border region between Texas and Mexico and includes influences from native food traditions, various European immigrant food prep techniques and some locally developed ideas.

I've read that at some point, Lebanese immigrants to Mexico also brought the shawarma/gyro with them and further contributed. I think it fills the same kind of food niche that Doner Kebabs fill in Europe, cheap, fast, unhealthy and filling. It's also an ideal foodtype for post-drunken late-night eating. Tacos seem to originate as a slang term used for mining charges in 18th century Mexican silver mines. At some point, somebody wrapped some meat in a tortilla and sold them as cheap laborer food.

Taco Bell was started by a guy named Glenn Bell back in the 1960s, he organized the menu, standardized on hard taco shells and a franchise model. They eventually discovered a kind of niche as a late night college food because you could easily get a couple days worth of food for cheaper than just about anywhere else -- and despite appearances has a very strong food safety record. Taco Bell is also the target of jokes about being low quality "garbage". (a common joke is that you can pick up your food at the counter and then go flush it down the toilet and cut out the middle man). Still, if you work late nights or went to college as an American, you probably ate a lot at Taco Bell and eventually developed a taste for it. If you've ever watched the movie "Demolition Man" it's a subtle joke throughout the movie that's culturally very funny to Americans.

I've never encountered a proper version of Tex-Mex outside of North America even though lots of places give it a good try. When I travel outside of the U.S. for long periods of time, it's the one kind of food I start to incessantly crave. I've noticed this among other Americans as well. Once, while doing work in Asia in an American enclave, a pop-up Taco Bell showed up charging 3 times the normal price and missing some ingredients and the line was 2 hours long.

They've tried to adopt "higher quality" ingredients and reform themselves in the past, but it's just not in their corporate DNA. More recently, they've decided to embrace their "crap food, fast and cheap" image and have developed an ever changing menu that brings in other junk food stuffs from sister brands. There's probably more food science than food in some of the menu items, but you can think of it as the cheapest molecular gastronomy meal you'll ever have.

Among immigrant friends to the U.S., most of them have their first taste of Taco Bell and think it's similarly revolting, but after a few years in the U.S. the cheapness and ubiquity of it kind of enters the diet. I know of a few people who returned to their home countries and have tried to work with Taco Bell to open franchises locally - and they all hated it the first time they ate it. My wife, a Korean immigrant, craves Taco Bell at times.