I am not even a native Chicagoan, though I lived there for many years, and I am personally offended anyone could have such a stance. I want each slice to be a meal.
I'm from Chicago and I like deep dish, but these big thin slices are also good. It's obvious what the default is: when I was a kid "pizza" meant Giordano's or Eduardo's or Lou Malnati's or The Medici, or Unos or Dues, etc. Thin crust was called "thin crust." This article uses the same convention.
edit: I think there was an exception for Reggio's. Maybe we thought of it as "pizza" because it's so dense and advertised as a "butter crust."
Or because it's close to home and way more affordable? Also, while winter sucks, I'll take a Chicago summer over both those places every single year.
I grew up here as well. No one thinks deep dish immediately when talking about getting pizza. It feels more like a once or twice a year delicacy than anyone's go-to pizza.