[pjmlp]

No, my answer is that the UNIX clones only bother to achieve POSIX compatibility and POSIX doesn't provide anything related to GUIs.

So, each UNIX clone project ends up replicating POSIX and doesn't move beyond what is actually yet another TWM clone with pretty graphics.

GNOME, KDE, Unity are the only ones that try to somehow modernize the experience and tend to get pretty vocal pushback.

The UNIX culture, is the culture of the command line and something like XFCE is probably the GUI a TWM user is willing to accept to manage its XTerms.