It is because that the "best" apps for Linux distros are written with GTK the reason for KDE being much less mainstream than Gnome?
That's the main thing I don't like about it. Also I don't get the depressive trend of washing out colors and turning the style into monochrome. What's wrong with colored icons?
I hope there will be a way to chose other styles and KDE will maintain the reputation of being very UI configurable.