Initial question was "Why is the world's largest In-n-Out in Barstow? Sure, it's on a major route halfway between LA and Vegas, but it's not like there aren't plenty of locations along the way."
Turns out it's to handle all the busloads of tourists going to the massive outlet mall next door, so followup question: why are busloads of tourists going to an outlet mall halfway between LA and Vegas? For that matter, why is there a massive outlet mall in Barstow?