Shutdown is in Settings because Settings is basically meant as the place to expose utility functions that are about the app / system itself, rather than the content that is the main purpose of the app / system. It's sort of like a Wikipedia "meta" page. That's why things like "About", "Rate and Review", "Feedback" and even "Help" (!) are also in Settings - they are about the app, they are not part of the content of the app.