KDE mainly has a a lack of decision making by the devs, & a lack of taste: the default theming, icons & panels are all fugly, and it takes a world of configuration work to make it look reasonable.

The appearance options are so complicated and multi-layered that it's hard to replicate simple changes, and even installing a pre-built theme isn't wholesale: Separate types of themes need to be applied in a few different places.

Then you finally have the problem of GTK apps: They look bad in 99% of KDE themes, and most users are using at least some GTK apps (Firefox, Chrome ).

Still better than other desktops, which do not even allow changing background color.

> GTK apps: They look bad in 99% of KDE themes

??? There is GTK engine which uses QT to render widgets. I really do not see any difference.

I use Chrome and only problem I have is new window placement, which is not really KDE problem. Chrome uses KDE dialogs and even KDE password manager.

Chrome stopped being a GTK+ app long time ago. They switched to their own internal toolkit(http://www.omgubuntu.co.uk/2014/05/google-chrome-35-linux-ar...).

Also, I am not sure why you say Firefox looks ugly in KDE - http://album.gnufied.org/firefox.png . I have made 0 modifications in KDE/GTK theming and firefox looks just fine under KDE.