It isn't. FreeBSD is for Internet servers and
people who want a desktop
that acts and feels like a classical UNIX workstation of the 90's.
Does xfce or KDE behave differently when running under FreeBSD? Pretty
much the same, really, as far as I can tell. Provided, your hardware is
supported, of course.
And linux is running one or the other internet server as well. At least
so the rumours go.