Why do people use XFCE?

I am new to Linux and have been trying out a bunch of different desktop environments. What I'm curious about is why do people use XFCE. From what I can see, the development is not as fast as the full featured desktop environments such as KDE and Gnome. Wayland support is not yet even the focus for the next release. Also KDE seems to be as efficient on resources as XFCE is. So why do people still use XFCE instead of using KDE and Gnome which rapidly push towards new features and development?