Thanks all for the insights.  Let me attempt a summary.

What it boils down to is that X arrived on Linux very early, because what the Linux hackers needed/wanted was a familiar terminal multiplexer. It seems that the pattern persists till the present day (and yes, it matches with my own dev setup/needs). I wonder to what extent this is a generational thing though. Maybe today’s twenty-somethings spend their days in front of Xcode, VStudio, Eclipse, etc. more than using multiple terminals.

This ties in with another observation on early window systems. The earliest Unix window system that I could find (i.e. documented) was NUnix from 1981/82. Its desktop was designed around the idea of a dozen or so top level windows, each one being either a shell window or a graphics canvas, with no real concept of a widget set, dialogs, etc., or even of sub-windows. This paradigm seems to have been more or less the same in the Blit terminal, and carried through in MGR, Mux and even as late as 8 1/2. In the context where this serves the needs of core user group, such makes sense.

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It is in stark contrast with developments at the lower/consumer end of the market. The original Mac, GEM and Windows all placed much more emphasis on being a graphical user interface, with standard widgets and UI design elements. On Unix and X it remained a mess. It seems that this was both for technical reasons (X not imposing a standard) and for economic reasons (the Unix wars). Linux then inherited the mess and the core user/developer demographic had no need/wish/time to fix it.

It makes me wonder when true graphical applications started to appear for X / Unix / Linux (other than stuff like terminal, clock, calculator, etc.). The graphical browser certainly is one (1993). StarOffice and Applix seem to have arrived around 1995. Anything broadly used before that?