I wouldn't say that either GNOME or KDE focus on mobile.
Both communities take steps to widen their portfolio towards mobile, e.g. by making UI and application cores less interdependent and thus allowing mobile UIs to use the same core.
I would bet that a majority of contributors do not even own a device that would make a viable host for the application they are working on.
If mobile were a priority for more than a handful of developers we would see way larger availability of GNOME and KDE apps in mobile app stores.