It was midwifed by the rise of factories:
[T]ortillas, like donuts, are best eaten fresh, preferably within a few hours off the griddle. In Mexico, tortilla factories have been largely a cottage industry, conveniently located on any street corner, and operating sporadically throughout the day for customers who line up before breakfast, lunch, and dinner. This just-in-time business model, however, fit poorly in the postwar "Fordist" era of giant factories pursuing economies of scale. Mass production was needed to achieve profits on low-value commodities, and there are few consumer goods cheaper than a corn tortilla. Commercial supplies of fresh tortillas were simply uneconomical in markets without regular demand from knowledgeable consumers, which basically meant everywhere except Mexico, Central America, and a few cities in the United States. By contrast, taco shells could be produced in bulk, wrapped in plastic, stored in warehouses, and shipped around the world, albeit with some breakage.
The Dish 