As I said -- Same reason I love it.

That system control panel app with all its billions of options and everything being customizable and change-able is very good if you are a user who a. WANTS to customize everything b. Either knows how or is willing to learn.

Most beginners aren't after that. They want something that is somewhat familiar and that works well. And while, sure, Plasma's defaults are pretty good... I can totally see a newbie user opening up KCM and immediately becoming overwhelmed. Another user here even mentioned how much time they wasted because all those choices actually got in the way of them getting stuff done