Counter-question: why should the UI style even be defined by your platform, and not by the user? Why can't I install UI themes which makes the UI look like wha

Counter-question: why should the UI style even be defined by your platform, and not by the user? Why can't I install UI themes which makes the UI look like whatever I want? Why does the user interface of the Apple user next to me have to look exactly the same as mine? (I'm also mainly an Apple user, and I don't like some 'traditional' Linux desktop clunkiness - mainly related to the touchpad - but criticizing a desktop environment (which the user is free to install or uninstall) for its looks is a bit ridiculous - especially from a user of a system where replacing the desktop environment isn't even possible).