LXAppearance not working under GDM

When selecting GDM as the Display Manager, the theme switches to Adwaita and I can’t switch it to anything else using LXAppearance. I can see that LXA does change ~/.gtkrc-2.0 as expected, but somehow the system doesn’t pick it up.

Filing this under i3wm because that’s the WM I use, but this seems to be a bug within GDM or something similar, since using another DM such as lightdm solves this.

Just found a workaround involving these terminal commands:

gsettings set org.gnome.desktop.interface gtk-theme "Arc-Dark"
gsettings set org.gnome.desktop.wm.preferences theme "Arc-dark"
gsettings set org.gnome.desktop.interface icon-theme "Arc-X-D"

lxappearance was driving me crazy. Thunar especially.

But why does this work?
just for my understanding.
Where does gnome come from?

Please don’t respond to two year old threads. If you have an issue feel free to start a new post.