Because, once again, extensions and quicks fixes doesn’t provide the same experience as built in features. Eg. GNOME 3.28 removed desktop icons and the extensions currently available don’t provide the same polished experience.
Fair enough. Though if you’ve not tried a lot of these extensions recently I’d bet you’d be surprised with the quality that some of them have nowadays. Ubuntu for example uses a handful of GNOME extensions to replace lost functionality like taskbar icons and desktop icons with good enough quality that most of their users don’t even notice it was ever missing.