Hi!

The trick is that etc/profile exports environment variables for the
packages that explicitly consume them, not for packages that are
consumed by others.

I don't know about Xfce, so I'll give you an example with pkg-config: if
you install just webkitgtk to a profile, its lib/pkgconfig/*.pc files
won't be detected by a `pkg-config` executable (that comes from a
different profile).  If you include `pkg-config` itself in the profile,
then the profile *.pc files will be found.

I suppose that for Xfce you need to install a component that looks up
XDG_DATA_DIRS.

Hope that helps!

-- 
Pierre Neidhardt
https://ambrevar.xyz/