it onsume quite more power than all other DEs. for me this is important as my pc is actually also my htpc.
and there is also ana dditional personal antipathy: i know and used kde since its early 2.x versions. and it was horrible. it was like using windows 3.1 on linux: bloated with a lot of half done features, unstable, slow.... it ket that way all they way to end 3.x.
of course this may have changed meanwhile with 4.x. can't tell this as i only tried kde 4 once a year ago and i ditched it due to its power consumption and higher cpu/gpu usage.
i also do not like may of its "features" and am too lazy to start customizing every thing "back" to get something i like. why should i....
meanwhile, even though there are also quite some things i dislike or am missing on gnome, i very like the concept of gnome shell. though this is a questuion of taste.
p.s. just in case somebody gets me wrong: my bad experience probalby isn't upt to date anymore. but this is own of my reasons for disliking kde.
but i am thankfull kde exists as it attracts a lot of other users. i like having many options that do please many users.
so as much as i personally dislike kde, if many enjoy it than i am happy it exists