I’ve only had St Louis pizza in St Louis once, and the big difference is the cheese. I didn’t like it, but certainly a lot of people do like it or it wouldn’t survive as a style of pizza.

Edit - Wikipedia says that St Louis pizza crust doesn’t have yeast in it. Chicago thin crust definitely uses yeast.

Provel isn't worthy of using the word "cheese" to describe it. (said lovingly as someone who worked in STL and was often handed pies of "office pizza" from Imo's.)

Each Imo’s franchise is independently owned, and uses either Provel or cheaper “Zesty Pizza Loaf” depending on location.

Now that I think about it, it’s like a white, grainy, Velveeta. One of the biggest problems with a cracker-thin crust is that you need to eat twice as much (or more) to get full, and it’s not any cheaper, but Imo’s does lay strips of bacon across their Deluxe and I’m a basic bitch.