Why Do Users Choose KDE?
Popularity polls for software are questionable indicators at best. However, with KDE receiving just under a third of the votes in LinuxQuestion's Members Choice for 2011 and 2012 and in Linux Journal's 2013 Readers' Choice Awards, there's enough consistency to call KDE the most popular Linux desktop environment.
Admittedly, if you add all the choices that use GNOME technology (Cinnamon, GNOME, Mate, and Unity), then KDE loses its position. But if you consider a desktop environment as a combination of both the shell and the underlying technology, KDE's position is unchallenged. At a time when half a dozen choices are available, KDE's one-third is probably as close to dominance as any desktop is likely to get.