Any software from a big company like Uber, Facebook, Google, etc. is far more complex than what you see. There are typically dozens of features and experiments rolled out to some users and not others. There is also a lot of work necessary to serve so many different markets, such as localization and internationalization. Furthermore, in Uber's case they have a lot more iOS applications than the ones riders use. In terms of complexity, Uber iOS apps are probably comparable to Facebook's apps.