Ask any seasoned jailbreaker and they will be able to tell you that the Cydia Store is literally jam-packed full of themes and aesthetic customizations which are designed to make an iPhone or iPad look as different as possible from the native iOS look. This isn't because designers believe there is anything wrong with the visuals in iOS per se, but jailbreaking is about the freedom to alter and change the way a stock iOS device looks and behaves, and producing themes is one way to drastically do that.
