Datamation's June 2012 article suggests that while GNOME has lost users, KDE has failed to pick them up:
Over the last fourteen months, discontent with Unity and the GNOME 3
series of releases have sent GNOME users galloping in all directions
in their search for alternatives. Xfce and Linux Mint's Cinnamon and
Mate in particular have benefited from this search. However, one
alternative that users have not considered to any extent is KDE.
Considering the years in which GNOME and KDE were considered the main
desktop environments for Linux, this trend is surprising at first.
Yet the trend seems hard to deny. Compare the results of
LinuxQuestion's Members Choice Awardswith the statistics from previous
years, and you’ll see that GNOME 3's release cost the desktop as much
as half its users.
However, the same comparison suggests that KDE is only at
three-quarters of its pre-KDE 4 popularity.
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Meanwhile, a question on unix.stackechange discusses why distros have historically bundled GNOME over KDE: Why do most linux distros default gnome?
It's difficult to get an accurate read on the popularity without relying on survey data.