It isn't a *package* management application. It's an *application*
management application, ie., it only handles packages that are desktop
applications (and therefore have desktop files associated with them).
I'm guessing power users that want to install other packages will need
to resort to the command line: yum/dnf/packagekit-cli. I'm not really
sure about this though. Someone else might know better.
All users can use yumex, if they want a package management gui, there can install every thing they want
but it is not installed by default in the Gnome desktop, so new user need to find out how to install it or how to