The reason the registry sucks is the same reason desktop operating systems generally suck: it isn’t sandboxed. Applications should not have a global view of the system and other applications. They should have their own container where they can do stuff, like write registry keys, write files, do stuff with whatever is exposed to the container. When the app is removed, everything inside that container goes with it. Of course, this is how mobile operating systems work, and they’re rock solid compared to Windows.

When you remove an app on Windows a bunch of garbage just gets orphaned on your system to the end of time.