Most everyone outside of Chicago has a distorted perception of what Chicago Deep Dish is and even more don't even know that we have thin crust.
Having never eaten a thin crust pizza in Chicago, here's my take on why people outside Chicago don't realize there is a "Chicago style" thin crust: There's nothing that clearly differentiates "Chicago style" thin crust pizza from pizza you can get in other cities, states, or regions. When I look through Chicago thin crust threads, I see pictures of pizzas that look a lot like what I can get at most pizza joints in Columbus or Dayton, Ohio, as well as what I've heard may be common in Pittsburgh.
If I buy a pizza in Columbus or Dayton, am I buying a Chicago style pizza? Hell no. But I bet it's pretty similar. And have you ever heard of Columbus style pizza or Dayton style pizza? I doubt it. If you want to know why you've never heard of Columbus style pizza or Dayton style pizza, I'd say it's probably because there's not much that differentiates it from pizzas you can get in plenty of other places, such as Chicago. So maybe what you consider Chicago style thin crust pizza is actually Midwest style pizza.
However, if I go to Chicago and buy a deep dish pizza, I'm gonna be served a pizza I can get almost nowhere outside of Chicago. That's why people outside of Chicago don't know there is thin crust pizza in Chicago. That, and how we've been "educated" by Food Network, the Travel Channel, and Uno's Chicago Grill (or whatever the chain is called these days).
Like I said, I've never eaten a thin crust pizza in Chicago, so I may be wrong.
But based on what I know about the history of pizza in the United States, if I take a few seconds to try to figure out why Chicago thin crust is similar to Ohio thin crust, one of my first thoughts is that the two styles of pizza likely have the same origin (or share the same branch on pizza's family tree). If so, that origin is probably not in Chicago; it's probably somewhere east of Chicago.
So maybe to eliminate all the confusion, instead of lumping Chicago style thin crust and Chicago deep dish into the same category, there should be a new category called something like Midwest Style Thin Crust.